3,376 research outputs found
Observations of the Extended Distribution of Ionized Hydrogen in the Plane of M31
We have used the Wisconsin H-Alpha Mapper (WHAM) to observe the spatially
extended distribution of ionized hydrogen in M31 beyond the stellar disk. We
obtained five sets of observations, centered near the photometric major axis of
M31, that extend from the center of the galaxy to just off the edge of the
southwestern HI disk. Beyond the bright stellar disk, but within the HI disk,
weak H-alpha is detected with an intensity I(H-alpha) = 0.05 (+0.01 / -0.02)
Rayleighs. Since M31 is inclined 77 degrees with respect to the line of sight,
this implies that the ambient intergalactic ionizing flux onto each side of M31
is Phi_0 <= 1.6 x 10^4 photons cm^-2 s^-1. Just beyond the outer boundary of
the HI disk we find no significant detection of H-alpha and place an upper
limit I(H-alpha) <= 0.019 Rayleighs.Comment: To appear in ApJ Letters; 12 pages, 4 figure
Exploring the views of students on the use of Facebook in university teaching and learning
Facebook use among students is almost ubiquitous; however, its use for formal academic purposes remains contested. Through an online survey monitoring student use of module Facebook pages and focus groups, this study explores studentsâ current academic uses of Facebook and their
views on using Facebook within university modules. Students reported using Facebook for academic purposes, notably peerâpeer communication around group work and assessment â a use not always conceptualised by students as learning. Focus groups revealed that students are not ready or equipped for the collaborative style of learning envisaged by the tutor and see Facebook as their personal domain, within which they
will discuss academic topics where they see a strong relevance and purpose, notably in connection with assessment. Students use Facebook for their own mutually deïŹned purposes and a change in student mind- and skill-sets is required to appropriate the collaborative learning beneïŹts of Facebook in formal educational contexts
Amorphous Systems in Athermal, Quasistatic Shear
We present results on a series of 2D atomistic computer simulations of
amorphous systems subjected to simple shear in the athermal, quasistatic limit.
The athermal quasistatic trajectories are shown to separate into smooth,
reversible elastic branches which are intermittently broken by discrete
catastrophic plastic events. The onset of a typical plastic event is studied
with precision, and it is shown that the mode of the system which is
responsible for the loss of stability has structure in real space which is
consistent with a quadrupolar source acting on an elastic matrix. The plastic
events themselves are shown to be composed of localized shear transformations
which organize into lines of slip which span the length of the simulation cell,
and a mechanism for the organization is discussed. Although within a single
event there are strong spatial correlations in the deformation, we find little
correlation from one event to the next, and these transient lines of slip are
not to be confounded with the persistent regions of localized shear --
so-called "shear bands" -- found in related studies. The slip lines gives rise
to particular scalings with system length of various measures of event size.
Strikingly, data obtained using three differing interaction potentials can be
brought into quantitative agreement after a simple rescaling, emphasizing the
insensitivity of the emergent plastic behavior in these disordered systems to
the precise details of the underlying interactions. The results should be
relevant to understanding plastic deformation in systems such as metallic
glasses well below their glass temperature, soft glassy systems (such as dense
emulsions), or compressed granular materials.Comment: 21 pages, 18 figure
A Method for Individual Source Brightness Estimation in Single- and Multi-band Data
We present a method of reliably extracting the flux of individual sources
from sky maps in the presence of noise and a source population in which number
counts are a steeply falling function of flux. The method is an extension of a
standard Bayesian procedure in the millimeter/submillimeter literature. As in
the standard method, the prior applied to source flux measurements is derived
from an estimate of the source counts as a function of flux, dN/dS. The key
feature of the new method is that it enables reliable extraction of properties
of individual sources, which previous methods in the literature do not. We
first present the method for extracting individual source fluxes from data in a
single observing band, then we extend the method to multiple bands, including
prior information about the spectral behavior of the source population(s). The
multi-band estimation technique is particularly relevant for classifying
individual sources into populations according to their spectral behavior. We
find that proper treatment of the correlated prior information between
observing bands is key to avoiding significant biases in estimations of
multi-band fluxes and spectral behavior, biases which lead to significant
numbers of misclassified sources. We test the single- and multi-band versions
of the method using simulated observations with observing parameters similar to
that of the South Pole Telescope data used in Vieira, et al. (2010).Comment: 11 emulateapj pages, 3 figures, revised to match published versio
Safety of overlapping inpatient orthopaedic surgery: A multicenter study
BackgroundAlthough overlapping surgery is used to maximize efficiency, more empirical data are needed to guide patient safety. We conducted a retrospective cohort study to evaluate the safety of overlapping inpatient orthopaedic surgery, as judged by the occurrence of perioperative complications.MethodsAll inpatient orthopaedic surgical procedures performed at 5 academic institutions from January 1, 2015, to December 31, 2015, were included. Overlapping surgery was defined as 2 skin incisions open simultaneously for 1 surgeon. In comparing patients who underwent overlapping surgery with those who underwent non-overlapping surgery, the primary outcome was the occurrence of a perioperative complication within 30 days of the surgical procedure, and secondary outcomes included all-cause 30-day readmission, length of stay, and mortality. To determine if there was an association between overlapping surgery and a perioperative complication, we tested for non-inferiority of overlapping surgery, assuming a null hypothesis of an increased risk of 50%. We used an inverse probability of treatment weighted regression model adjusted for institution, procedure type, demographic characteristics (age, sex, race, comorbidities), admission type, admission severity of illness, and clustering by surgeon.ResultsAmong 14,135 cases, the frequency of overlapping surgery was 40%. The frequencies of perioperative complications were 1% in the overlapping surgery group and 2% in the non-overlapping surgery group. The overlapping surgery group was non-inferior to the non-overlapping surgery group (odds ratio [OR], 0.61 [90% confidence interval (CI), 0.45 to 0.83]; p < 0.001), with reduced odds of perioperative complications (OR, 0.61 [95% CI, 0.43 to 0.88]; p = 0.009). For secondary outcomes, there was a significantly lower chance of all-cause 30-day readmission in the overlapping surgery group (OR, 0.67 [95% CI, 0.52 to 0.87]; p = 0.003) and shorter length of stay (e, 0.94 [95% CI, 0.89 to 0.99]; p = 0.012). There was no difference in mortality.ConclusionsOur results suggest that overlapping inpatient orthopaedic surgery does not introduce additional perioperative risk for the complications that we evaluated. The suitability of this practice should be determined by individual surgeons on a case-by-case basis with appropriate informed consent.Level of evidenceTherapeutic Level III. See Instructions for Authors for a complete description of levels of evidence
Formation and removal of alkylthiolate self-assembled monolayers on gold in aqueous solutions
We report the development of novel reagents and approaches for generating recyclable biosensors. The use of aqueous media for the formation of protein binding alkylthiolate monolayers on Au surfaces results in accelerated alkylthiolate monolayer formation and improvement in monolayer integrity as visualized by fluorescence microscopy and CV techniques. We have also developed an electrocleaning protocol that is compatible with microfluidics devices, and this technique serves as an on-chip method for cleaning Au substrates both before and after monolayer formation. The techniques for the formation and dissociation of biotinylated SAMs from aqueous solvents reported here may be applied towards the development of Au-based sensor devices and microfluidics chips in the future. A potential use of these devices includes the specific capture and triggered release of target cells, proteins, or small molecules from liquid samples
Mapping Children's Discussions of Evidence in Science to Assess Collaboration and Argumentation
The research reported in this paper concerns the development of children's skills of interpreting and evaluating evidence in science. Previous studies have shown that school teaching often places limited emphasis on the development of these skills, which are necessary for children to engage in scientific debate and decision-making. The research, undertaken in the UK, involved four collaborative decision-making activities to stimulate group discussion, each was carried out with five groups of four children (10-11 years old). The research shows how the children evaluated evidence for possible choices and judged whether their evidence was sufficient to support a particular conclusion or the rejection of alternative conclusions. A mapping technique was developed to analyse the discussions and identify different "levels" of argumentation. The authors conclude that suitable collaborative activities that focus on the discussion of evidence can be developed to exercise children's ability to argue effectively in making decisions
The Distance to the Large Magellanic Cloud from the Eclipsing Binary HV2274
The distance to the Large Magellanic Cloud (LMC) is crucial for the
calibration of the Cosmic Distance Scale. We derive a distance to the LMC based
on an analysis of ground-based photometry and HST-based spectroscopy and
spectrophotometry of the LMC eclipsing binary system HV2274. Analysis of the
optical light curve and HST/GHRS radial velocity curve provides the masses and
radii of the binary components. Analysis of the HST/FOS UV/optical
spectrophotometry provides the temperatures of the component stars and the
interstellar extinction of the system. When combined, these data yield a
distance to the binary system. After correcting for the location of HV2274 with
respect to the center of the LMC, we find d(LMC) = 45.7 +/- 1.6 kpc or DM(LMC)
= 18.30 +/- 0.07 mag. This result, which is immune to the metallicity-induced
zero point uncertainties that have plagued other techniques, lends strong
support to the ``short'' LMC distance scale as derived from a number of
independent methods.Comment: 6 pages, including 2 pages of figures. Newly available optical (B and
V) photometry has revealed -- and allowed the elimination of -- a systematic
error in the previously reported determination of E(B-V) for HV2274. The new
result is E(B-V) = 0.12 mag (as compared to the value of 0.083 reported in
the original submission) and produces a DECREASE in the distance modulus of
HV2274 by 0.12 mag. ApJ Letters, in pres
ASCA Observation of an X-Ray-Luminous Active Nucleus in Markarian 231
We have obtained a moderately long (100 kilosecond) ASCA observation of the
Seyfert 1 galaxy Markarian 231, the most luminous of the local ultraluminous
infrared galaxy (ULIRG) population. In the best-fitting model we do not see the
X-ray source directly; the spectrum consists of a scattered power-law component
and a reflection component, both of which have been absorbed by a column N_H
\approx 3 X 10^(22)/cm^2. About 3/4 of the observed hard X-rays arise from the
scattered component, reducing the equivalent width of the iron K alpha line.
The implied ratio of 1-10 keV X-ray luminosity to bolometric luminosity,
L_x/L_bol \sim 2%, is typical of Sy 1 galaxies and radio-quiet QSOs of
comparable bolometric luminosities, and indicates that the bolometric
luminosity is dominated by the AGN. Our estimate of the X-ray luminosity also
moves Mrk 231 in line with the correlations found for AGN with extremely strong
Fe II emission. A second source separated by about 2 arcminutes is also clearly
detected, and contributes about 25% of the total flux.Comment: 11 pages, 3 figures; to appear in ApJ Letter
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