774 research outputs found
The Origin of the 4.5 micron Excess from Dwarf Galaxies
Dwarf galaxies tend to have redder [3.6 micron] - [4.5 micron] Spitzer
broadband colors than spirals. To investigate this effect, for a large sample
of dwarf galaxies we combine Spitzer fluxes with data at other wavelengths and
compare to population synthesis models. Lower metallicity systems are found to
have redder [3.6] - [4.5] colors on average, but with considerable scatter. The
observed range in [3.6] - [4.5] color is too large to be accounted for solely
by variations in stellar colors due to age or metallicity differences;
interstellar effects must contribute as well. For the reddest systems, the 4.5
micron luminosity may not be a good tracer of stellar mass. We identify three
factors that redden this color in dwarfs. First, in some systems, strong
Br-alpha emission contributes significantly to the 4.5 micron emission. Second,
in some cases high optical depths lead to strong reddening of the starlight in
the Spitzer bands. Third, in some galaxies, the nebular continuum dominates the
4.5 micron flux, and in extreme cases, the 3.6 micron flux as well. The harder
UV radiation fields in lower metallicity systems produce both more gaseous
continuum in the infrared and more Br-alpha per star formation rate. The
combination of these three factors can account for the 4.5 micron excess in our
sample galaxies, thus it is not necessary to invoke a major contribution from
hot dust to the 4.5 micron band. However, given the uncertainties, we are not
able to completely rule out hot dust emission at 4.5 micron. More spectroscopic
observations in the 3 - 5 micron range are needed to disentangle these effects.Comment: Accepted by Astronomical Journa
Advancing imaging technologies for patients with spinal pain : with a focus on whiplash injury
Background: Radiological observations of soft-tissue changes that may relate to clinical symptoms in patients with traumatic and non-traumatic spinal disorders are highly controversial. Studies are often of poor quality and findings are inconsistent. A plethora of evidence suggests some pathoanatomical findings from traditional imaging applications are common in asymptomatic participants across the life span, which further questions the diagnostic, prognostic, and theranostic value of traditional imaging. Although we do not dispute the limited evidence for the clinical importance of most imaging findings, we contend that the disparate findings across studies may in part be due to limitations in the approaches used in assessment and analysis of imaging findings.
Purpose: This clinical commentary aimed to (1) briefly detail available imaging guidelines, (2) detail research-based evidence around the clinical use of findings from advanced, but available, imaging applications (eg, fat and water magnetic resonance imaging and magnetization transfer imaging), and (3) introduce how evolving imaging technologies may improve our mechanistic understanding of pain and disability, leading to improved treatments and outcomes.
Study Design/Setting: A non-systematic review of the literature is carried out.
Methods: A narrative summary (including studies from the authors' own work in whiplash injuries) of the available literature is provided.
Results: An emerging body of evidence suggests that the combination of existing imaging sequences or the use of developing imaging technologies in tandem with a good clinical assessment of modifiable risk factors may provide important diagnostic information toward the exploration and development of more informed and effective treatment options for some patients with traumatic neck pain.
Conclusions: Advancing imaging technologies may help to explain the seemingly disconnected spectrum of biopsychosocial signs and symptoms of traumatic neck pain
Event Representations for Automated Story Generation with Deep Neural Nets
Automated story generation is the problem of automatically selecting a
sequence of events, actions, or words that can be told as a story. We seek to
develop a system that can generate stories by learning everything it needs to
know from textual story corpora. To date, recurrent neural networks that learn
language models at character, word, or sentence levels have had little success
generating coherent stories. We explore the question of event representations
that provide a mid-level of abstraction between words and sentences in order to
retain the semantic information of the original data while minimizing event
sparsity. We present a technique for preprocessing textual story data into
event sequences. We then present a technique for automated story generation
whereby we decompose the problem into the generation of successive events
(event2event) and the generation of natural language sentences from events
(event2sentence). We give empirical results comparing different event
representations and their effects on event successor generation and the
translation of events to natural language.Comment: Submitted to AAAI'1
Large-scale Star Formation Triggering in the Low-mass Arp 82 System: A Nearby Example of Galaxy Downsizing Based on UV/Optical/Mid-IR Imaging
As part of our Spitzer Spirals, Bridges, and Tails project to help understand
the effects of galaxy interactions on star formation, we analyze GALEX
ultraviolet, SARA optical, and Spitzer infrared images of the interacting
galaxy pair Arp 82 (NGC 2535/6) and compare to a numerical simulation of the
interaction. We investigate the multiwavelength properties of several
individual star forming complexes (clumps). Using optical and UV colors,
EW(Halpha), and population synthesis models we constrain the ages of the clumps
and find that the median clump age is about 12 Myr. The clumps have masses
ranging from a few times 10^6 to 10^9 solar masses. In general, the clumps in
the tidal features have similar ages to those in the spiral region, but are
less massive. The 8 micron and 24 micron luminosities are used to estimate the
far-infrared luminosities and the star formation rates of the clumps. The total
clump star formation rate is 2.0+/-0.8 solar masses per year, while the entire
Arp 82 system is forming stars at a rate of 4.9+/-2.0 solar masses per year. We
find, for the first time, stars in the HI arc to the southeast of the NGC 2535
disk. Population synthesis models indicate that all of the observed populations
have young to intermediate ages. We conclude that although the gas disks and
some old stars may have formed early-on, the progenitors are late-type or low
surface brightness and the evolution of these galaxies was halted until the
recent encounter.Comment: Accepted for publication in the AJ, 22 Figures, 5 Table
Stochastic `Beads on a String' in the Accretion Tail of Arp 285
We present Spitzer infrared, GALEX UV, and SDSS and SARA optical images of
the peculiar interacting galaxy pair Arp 285 (NGC 2856/4), and compare with a
new numerical model of the interaction. We estimate the ages of clumps of star
formation in these galaxies using population synthesis models, carefully
considering the uncertainties on these ages. This system contains a striking
example of `beads on a string': a series of star formation complexes ~1 kpc
apart. These `beads' are found in a tail-like feature that is perpendicular to
the disk of NGC 2856, which implies that it was formed from material accreted
from the companion NGC 2854. The extreme blueness of the optical/UV colors and
redness of the mid-infrared colors implies very young stellar ages (~4 - 20
Myrs) for these star forming regions. Spectral decomposition of these `beads'
shows excess emission above the modeled stellar continuum in the 3.6 micron and
4.5 micron bands, indicating either contributions from interstellar matter to
these fluxes or a second older stellar population. These clumps have -12.0 <
M(B) < -10.6, thus they are less luminous than most dwarf galaxies. Our model
suggests that bridge material falling into the potential of the companion
overshoots the companion. The gas then piles up at apo-galacticon before
falling back onto the companion, and star formation occurs in the pile-up. A
luminous (M(B) ~ -13.6) extended (FWHM ~ 1.3 kpc) `bright spot' is visible at
the northwestern edge of the NGC 2856 disk, with an intermediate stellar
population (400 - 1500 Myrs). Our model suggests that this feature is part of a
expanding ripple-like `arc' created by an off-center ring-galaxy-like collision
between the two disks.Comment: Accepted by the Astronomical Journal. For color figures and appendix
material, go
tohttp://www.etsu.edu/physics/bsmith/research/sg/arp285/arp285.htm
A review of how we assess denitrification in oyster habitats and proposed guidelines for future studies
Excess nitrogen (N) loading and resulting eutrophication plague coastal ecosystems globally. Much work is being done to remove N before it enters coastal receiving waters, yet these efforts are not enough. Novel techniques to remove N from within the coastal ecosystem are now being explored. One of these techniques involves using oysters and their habitats to remove N via denitrification. There is substantial interest in incorporating oyster-mediated enhancement of benthic denitrification into N management plans and trading schemes. Measuring denitrification, however, is expensive and time consuming. For large-scale adoption of oyster-mediated denitrification into nutrient management plans, we need an accurate model that can be applied across ecosystems. Despite significant effort to measure and report rates of denitrification in oyster habitats, we are unable to create such a model, due to methodological differences between studies, incomplete data reporting, and inconsistent measurements of environmental variables that may be used to predict denitrification. To make a model that can predict denitrification in oyster habitats a reality, a common sampling and reporting scheme is needed across studies. Here, we provide relevant background on how oysters may stimulate denitrification, and the importance of oyster-mediated denitrification in remediating excess N loading to coastal systems. We then summarize methods commonly used to measure denitrification in oyster habitats, discuss the importance of various environmental variables that may be useful for predicting denitrification, and present a set of guidelines for measuring denitrification in oyster habitats, allowing development of models to support incorporation of oyster-mediated denitrification into future policy decisions
Cholesterol-sensitive Cdc42 activation regulates actin polymerization for endocytosis via the GEEC pathway
Glycosyl-phosphatidylinositol (GPI)-anchored proteins (GPI-APs) are present at the surface of living cells in cholesterol dependent nanoscale clusters. These clusters appear to act as sorting signals for the selective endocytosis of GPI-APs via a Cdc42-regulated, dynamin and clathrin-independent pinocytic pathway called the GPI-AP-enriched early endosomal compartments (GEECs) pathway. Here we show that endocytosis via the GEECs pathway is inhibited by mild depletion of cholesterol, perturbation of actin polymerization or overexpression of the Cdc42/Rac-interactive-binding (CRIB) motif of neural Wiskott-Aldrich syndrome protein (N-WASP). Consistent with the involvement of Cdc42-based actin nanomachinery, nascent endocytic vesicles containing cargo for the GEEC pathway co-localize with fluorescent protein-tagged isoforms of Cdc42, CRIB domain, N-WASP and actin; high-resolution electron microscopy on plasma membrane sheets reveals Cdc42-labelled regions rich in green fluorescent protein-GPI. Using total internal reflection fluorescence microscopy at the single-molecule scale, we find that mild cholesterol depletion alters the dynamics of actin polymerization at the cell surface by inhibiting Cdc42 activation and consequently its stabilization at the cell surface. These results suggest that endocytosis into GEECs occurs through a cholesterol-sensitive, Cdc42-based recruitment of the actin polymerization machinery
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