1,157 research outputs found
The Modern Academic Library: Space to Learn
Over the last two decades academic libraries in the United States have experienced a paradigm shift from book-centered spaces to learning-centered spaces as they work to provide services and resources in the new ways that users consume information. This article discusses the results of a survey conducted in early 2017 of South Carolina academic libraries to study this larger trend moving to learning-centered spaces. Forty two academic library administrators responded and shared how they are re-purposing their library spaces as they work to improve student and faculty user experiences
Spectral energy distribution modelling of Southern candidate massive protostars using the Bayesian inference method
Concatenating data from the millimetre regime to the infrared, we have
performed spectral energy distribution modelling for 227 of the 405 millimetre
continuum sources of Hill et al. (2005) which are thought to contain young
massive stars in the earliest stages of their formation. Three main parameters
are extracted from the fits: temperature, mass and luminosity. The method
employed was Bayesian inference, which allows a statistically probable range of
suitable values for each parameter to be drawn for each individual protostellar
candidate. This is the first application of this method to massive star
formation.
The cumulative distribution plots of the SED modelled parameters in this work
indicate that collectively, the sources without methanol maser and/or radio
continuum associations (MM-only cores) display similar characteristics to those
of high mass star formation regions. Attributing significance to the marginal
distinctions between the MM-only cores and the high-mass star formation sample
we draw hypotheses regarding the nature of the MM-only cores, including the
possibility that the population itself is comprised of different types of
source, and discuss their role in the formation scenarios of massive star
formation. In addition, we discuss the usefulness and limitations of SED
modelling and its application to the field. From this work, it is clear that
within the valid parameter ranges, SEDs utilising current far-infrared data can
not be used to determine the evolution of massive protostars or massive young
stellar objects.Comment: 16 pages, 3 figures, 5 tables : accepted by MNRA
Recommended from our members
Twentieth century secular decrease in the atmospheric potential gradient
Current flowing in the global atmospheric electrical circuit (AEC) substantially decreased during the twentieth century. Fair-weather potential gradient (PG) observations in Scotland and Shetland show a previously unreported annual decline from 1920 to 1980, when the measurements ceased. A 25% reduction in PG occurred in Scotland 1920â50, with the maximum decline during the winter months. This is quantitatively explained by a decrease in cosmic rays (CR) increasing the thunderstorm-electrosphere coupling resistance, reducing the ionospheric potential VI. Independent measurements of VI also suggest a reduction of 27% from 1920â50. The secular decrease will influence fair weather atmospheric electrical parameters, including ion concentrations and aerosol electrification. Between 1920â50, the PG showed a negative correlation with global temperature, despite the positive correlation found recently between surface temperature and VI. The 1980s stabilisation in VI may arise from compensation of the continuing CR-induced decline by increases in global temperature and convective electrification
The very bright SCUBA galaxy count: looking for SCUBA galaxies with the Mexican Hat Wavelet
We present the results of a search for bright high-redshift galaxies in two
large SCUBA scan-maps of Galactic regions. A Mexican Hat Wavelet technique was
used to locate point sources in these maps, which suffer high foreground
contamination as well as typical scan-map noise signatures. A catalogue of
point source objects was selected and observed again in the submillimetre
continuum, and in HCO+ (3->2) at zero redshift to rule out Galactic sources. No
extragalactic sources were found. Simulations show that the survey was
sensitive to sources with fluxes > 50 mJy, depending on the local background.
These simulations result in upper limits on the 850-micron counts of SCUBA
galaxies of 53 per square degree at 50 mJy and 2.9 per square degree at 100
mJy.Comment: Accepted by MNRA
Mapping the submillimeter spiral wave in NGC 6946
We have analysed SCUBA 850\mum images of the (near) face-on spiral galaxy NGC
6946, and found a tight correlation between dust thermal emission and molecular
gas. The map of visual optical depth relates well to the distribution of
neutral gas (HI+H2) and implies a global gas-to-dust ratio of 90. There is no
significant radial variation of this ratio: this can be understood, since the
gas content is dominated by far by the molecular gas. The latter is estimated
through the CO emission tracer, which is itself dependent on metallicity,
similarly to dust emission. By comparing the radial profile of our visual
optical depth map with that of the SCUBA image, we infer an emissivity (dust
absorption coefficient) at 850\mum that is 3 times lower than the value
measured by COBE in the Milky Way, and 9 times lower than in NGC 891. A
decomposition of the spiral structure half way out along the disk of NGC 6946
suggests an interarm optical depth of between 1 and 2. These surprisingly high
values represent 40-80% of the visual opacity that we measure for the arm
region (abridged).Comment: 12 pages, 9 figures, accepted in A&
Renewed diversification is associated with new ecological opportunity in the N eotropical turtle ants
Ecological opportunity, defined as access to new resources free from competitors, is thought to be a catalyst for the process of adaptive radiation. Much of what we know about ecological opportunity, and the larger process of adaptive radiation, is derived from vertebrate diversification on islands. Here, we examine lineage diversification in the turtle ants ( C ephalotes ), a speciesârich group of ants that has diversified throughout the N eotropics. We show that crown group turtle ants originated during the E ocene (around 46 mya), coincident with global warming and the origin of many other clades. We also show a marked lineageâwide slowdown in diversification rates in the M iocene. Contrasting this overall pattern, a species group associated with the young and seasonally harsh C hacoan biogeographic region underwent a recent burst of diversification. Subsequent analyses also indicated that there is significant phylogenetic clustering within the C hacoan region and that speciation rates are highest there. Together, these findings suggest that recent ecological opportunity, from successful colonization of novel habitat, may have facilitated renewed turtle ant diversification. Our findings highlight a central role of ecological opportunity within a successful continental radiation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/102632/1/jeb12300-sup-0001-AppendixFigS1-S4-TableS1-S4.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/102632/2/jeb12300.pd
The Nature of Nonthermal X-ray Filaments Near the Galactic Center
Recent Chandra and XMM-{\it Newton} observations reported evidence of two
X-ray filaments G359.88-0.08 (SgrA-E) and G359.54+0.18 (the ripple filament)
near the Galactic center. The X-ray emission from these filaments has a
nonthermal spectrum and coincides with synchrotron emitting radio sources.
Here, we report the detection of a new X-ray feature coincident with a radio
filament G359.90-0.06 (SgrA-F) and show more detailed VLA, Chandra and BIMA
observations of the radio and X-ray filaments. In particular, we show that
radio emission from the nonthermal filaments G359.90-0.06 (SgrA-F) and
G359.54+0.18 (the ripple) has a steep spectrum whereas G359.88-0.08 (SgrA-E)
has a flat spectrum. The X-ray emission from both these sources could be due to
synchrotron radiation. However, given that the 20 \kms molecular cloud, with
its intense 1.2mm dust emission, lies in the vicinity of SgrA-F, it is possible
that the X-rays could be produced by inverse Compton scattering of far-infrared
photons from dust by the relativistic electrons responsible for the radio
synchrotron emission. The production of X-ray emission from ICS allows an
estimate of the magnetic field strength of ~0.08 mG within the nonthermal
filament. This should be an important parameter for any models of the Galactic
center nonthermal filaments.Comment: 14 pages, 9 figures, in Cospar 2004 session E1.4; editors: Cara
Rakowski and Shami Chatterjee; "Young Neutron Stars and Supernova Remnants",
publication: Advances in Space Research (in press
Mapping Magnetic Fields in the Cold Dust at the Galactic Center
We report the detection of polarized emission in the vicinity of the Galactic
center for 158 positions within eight different pointings of the Hertz
polarimeter operating on the Caltech Submillimeter Observatory. These pointings
include positions 2 arcminutes offset to the E, NE, and NW of M-0.02-0.07;
positions to the SE and NW of the 20 km/s cloud (M-0.13-0.08), CO+0.02-0.02,
M+0.07-0.08, and M+0.11-0.08. We use these data in conjunction with previous
far-infrared and submillimeter polarization results to find that the direction
of the inferred magnetic field is related to the density of the molecular
material in the following way: in denser regions, the field is generally
parallel to the Galactic plane, whereas in regions with lower densities, the
field is generally perpendicular to the plane. This finding is consistent with
a model in which an initially poloidal field has been sheared into a toroidal
configuration in regions that are dense enough such that the gravitational
energy density is greater than the energy density of the magnetic field. Using
this model, we estimate the characteristic strength of the magnetic field in
the central 30 pc of our Galaxy to be a few mG
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