453 research outputs found
The Masses and Shapes of Dark Matter Halos from Galaxy-Galaxy Lensing in the CFHTLS
We present the first galaxy-galaxy weak lensing results using early data from
the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). These results are
based on ~22 sq. deg. of i' data. From this data, we estimate the average
velocity dispersion for an L* galaxy at a redshift of 0.3 to be 137 +- 11 km/s,
with a virial mass, M_{200}, of 1.1 +- 0.2 \times 10^{12} h^{-1} Msun and a
rest frame R-band mass-to-light ratio of 173 +- 34 h Msun/Lsun. We also
investigate various possible sources of systematic error in detail.
Additionally, we separate our lens sample into two sub-samples, divided by
apparent magnitude, thus average redshift. From this early data we do not
detect significant evolution in galaxy dark matter halo mass-to-light ratios
from a redshift of 0.45 to 0.27. Finally, we test for non-spherical galaxy dark
matter halos. Our results favor a dark matter halo with an ellipticity of ~0.3
at the 2-sigma level when averaged over all galaxies. If the sample of
foreground lens galaxies is selected to favor ellipticals, the mean halo
ellipticity and significance of this result increase.Comment: 12 pages, 11 figures, accepted to ApJ, uses emulateap
Mass-to-Light Ratios of Galaxy Groups from Weak Lensing
We present the findings of our weak lensing study of a sample of 116 CNOC2
galaxy groups. The lensing signal is used to estimate the mass-to-light ratio
of these galaxy groups. The best fit isothermal sphere model to our lensing
data has an Einstein radius of 0.88"+/-0.12", which corresponds to a
shear-weighted velocity dispersion of 245+/-18 km/s. The mean mass-to-light
ratio within 1 h^-1 Mpc is 185+/-28 h times solar in the B-band and is
independent of radius from the group center.
The signal-to-noise ratio of the shear measurement is sufficient to split the
sample into subsets of "poor" and "rich" galaxy groups. The poor galaxy groups
were found to have an average velocity dispersion of 193+/-38 km/s and a
mass-to-light ratio of 134+/-26 h times solar in the B-band, while the rich
galaxy groups have a velocity dispersion of 270+/-39 km/s and a mass-to-light
ratio of 278+/-42 h times solar in the B-band, similar to the mass-to-light
ratio of clusters. This steep increase in the mass-to-light ratio as a function
of mass, suggests that the mass scale of ~10^13 solar masses is where the
transition between the actively star-forming field environment and the
passively-evolving cluster environment occurs. This is the first such detection
from weak lensing.Comment: Accepted for publication in ApJ 6 pages, 6 figures, uses emulateap
Hot X-ray Onsets of Solar Flares
The study of the localized plasma conditions before the impulsive phase of a
solar flare can help us understand the physical processes that occur leading up
to the main flare energy release. Here, we present evidence of a hot X-ray
onset interval of enhanced isothermal plasma temperatures in the range of
10-15~MK up to tens of seconds prior to the flare's impulsive phase. This `hot
onset' interval occurs during the initial soft X-ray increase and prior to the
detectable hard X-ray emission. The isothermal temperatures, estimated by the
Geostationary Operational Environmental Satellite (GOES) X-ray sensor, and
confirmed with data from the Reuven Ramaty High Energy Solar Spectroscopic
Imager (RHESSI), show no signs of gradual increase, and the `hot onset'
phenomenon occurs regardless of flare classification or configuration. In a
small sample of four representative flare events we identify this early hot
onset soft X-ray emission mainly within footpoint and low-lying loops, rather
than with coronal structures, based on images from the Atmospheric Imaging
Assembly (AIA). We confirm this via limb occultation of a flaring region. These
hot X-ray onsets appear before there is evidence of collisional heating by
non-thermal electrons, and hence they challenge the standard flare heating
modeling techniques.Comment: Submitted to MNRAS 6 July 202
Services for Adults with an Autism Spectrum Disorder
Objective: The need for useful evidence about services is increasing as larger numbers of children identified with an autism spectrum disorder age toward adulthood. The objective of this review was to characterize the topical and methodological aspects of research on services for supporting success in work, education, and social participation among adults with an autism spectrum disorder and to propose recommendations for moving this area of research forward. Method: Review of literature published in English from 2000 to 2010.Results: We found that the evidence base about services for adults with an ASD is underdeveloped and can be considered a field of inquiry that is relatively unformed. Extant research does not reflect the demographic or impairment heterogeneity of the population, the range of services that adults with autism require in order to function with purposeful lives in the community, and the need for coordination across service systems and sectors. Conclusions: Future studies must examine issues related to cost and efficiency given the broader sociopolitical and economic context of service provision. Furthermore, future research needs to consider how demographic and impairment heterogeneity have implications for building an evidence base that will have greater external validity
Gathering Galaxy Distances in Abundance with Roman Wide-Area Data
The extragalactic distance scale is fundamental to our understanding of
astrophysics and cosmology. In recent years, the surface brightness fluctuation
(SBF) method, applied in the near-IR, has proven especially powerful for
measuring galaxy distances, first with HST and now with a new JWST program to
calibrate the method directly from the tip of the red giant branch (TRGB). So
far, however, the distances from space have been gathered slowly, one or two at
a time. With the Roman Space Telescope, we have the opportunity to measure
uniformly high-quality SBF distances to thousands of galaxies out to hundreds
of Mpc. The impact of these data on cosmology and galaxy studies depends on the
specifics of the survey, including the filter selection, exposure depth, and
(especially) the sky coverage. While the baseline HLWAS survey in four filters
plus the grism would yield useful data, the impact would be limited by the
relatively small area. A more optimal approach would concentrate on the most
efficient passband (F146), adopt an exposure time sufficient to measure good
quality distances well out into the Hubble flow, and then maximize the sky
coverage within the total time constraints. Grism observations over the same
area can provide the needed information on redshifts and spectral energy
distributions for compact sources, while colors for larger objects can be
obtained from lower resolution surveys. The proposed plan will enable accurate
determination of the physical properties of thousands of nearby galaxies, an
independent measure of the Hubble constant with negligible statistical
error, and competitive constraints on .
The resulting data set will be a phenomenal resource for a wide range of
studies in astrophysics and cosmology.Comment: 5 pages; submitted to the call for Roman Core Community Survey white
paper
Graphene Oxide Reduces the Hydrolytic Degradation in Polyamide-11
Graphene oxide (GO) was incorporated into polyamide-11 (PA11) via in-situ polymerization. The GO-PA11 nano-composite had elevated resistance to hydrolytic degradation. At a loading of 1 mg/g, GO to PA11, the accelerated aging equilibrium molecular weight of GO-PA11 was higher (33 and 34 kg/mol at 100 and 120 C, respectively) compared to neat PA11 (23 and 24 kg/mol at 100 and 120 C, respectively). Neat PA11 had hydrolysis rate constants (kH) of 2.8 and 12 ( 10(exp -2) day(exp -1)) when aged at 100 and 120 C, respectively, and re-polymerization rate constants (kP) of 5.0 and 23 ( 10(exp -5) day(exp -1)), respectively. The higher equilibrium molecular weight for GO-PA11 loaded at 1 mg/g was the result of a decreased kH, 1.8 and 4.5 ( 10(exp -2) day(exp -1)), and an increased kP, 10 and 17 ( 10(exp -5) day(exp -1)) compared with neat PA11 at 100 and 120 C, respectively. The decreased rate of degradation and resulting 40% increased equilibrium molecular weight of GO-PA11 was attributed to the highly asymmetric planar GO nano-sheets that inhibited the molecular mobility of water and the polymer chain. The crystallinity of the polymer matrix was similarly affected by a reduction in chain mobility during annealing due to the GO nanoparticles' chemistry and highly asymmetric nano-planar sheet structure
The Puzzle of Partial Resource Use by a Parasitoid Wasp
When there is conspicuous underexploitation of a limited resource, it is worth asking, what mechanisms allow presumably valuable resources to be left unused? Evolutionary biologists have generated a wide variety of hypotheses to explain this, ranging from interdemic group selection to selfishly prudent individual restraint. We consider a situation in which, despite high intraspecific competition, individuals leave most of a key resource unexploited. The parasitic wasp that does this finds virtually all host egg clusters in a landscape but parasitizes only about a third of the eggs in each and then leaves a deterrent mark around the cluster. We first test—and reject—a series of system-specific simple constraints that might limit full host exploitation, such as asynchronous maturation of host eggs. We then consider classical hypotheses for the evolution of restraint. Prudent predation and bet-hedging fail as explanations because the wasp lives as a large, well-mixed population. Additionally, we find no individual benefits to the parasitoid of developing in a sparsely parasitized host nest.However, an optimal foragingmodel, including empirically measured costs of superparasitism and hyperparasitism, can explain through individual selection both the consistently low rate of parasitism and deterrent marking.Peer reviewe
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