366 research outputs found
Student Attitudes to an Online, Peer-instruction, Revision Aid in Science Education
Peer instruction has been shown to have a positive effect on studentsâ engagement and learning. However, many of the techniques designed to incorporate peer instruction into the student experience are very heavy on resources. PeerWise is a free, low-maintenance, web-tool designed to allow peer instruction between students within a large class group. Students can write, answer and discuss Multiple Choice Questions (MCQs) based on their work in-class.
In this study, we introduce PeerWise to a wide and varied cohort of science students (N=509) across different disciplines, undergraduate years, levels (certificate to honours degree) and institutes. The attitudes of the students to PeerWise are probed using a questionnaire (356 respondents). This includes responses to Likert-style questions and thematic analysis carried out on free-text responses.
It is found that the students are positive about the addition of PeerWise and recognise the advantages of the software in their learning. They recognise, and articulate, the advantages of PeerWise as an active-learning, peer-instruction revision tool. Further advantages and disadvantages are discussed, such as the flooding of system with easy and/or repetitive questions. Overall, the results are positive and are very similar across the varied class groups. In this study, PeerWise performs as free and low-maintenance software that allows the addition of (another) peer-instruction aspect to modules
Photoionization of High Altitude Gas in a Supernova-Driven Turbulent Interstellar Medium
We investigate models for the photoionization of the widespread diffuse
ionized gas in galaxies. In particular we address the long standing question of
the penetration of Lyman continuum photons from sources close to the galactic
midplane to large heights in the galactic halo. We find that recent
hydrodynamical simulations of a supernova-driven interstellar medium have low
density paths and voids that allow for ionizing photons from midplane OB stars
to reach and ionize gas many kiloparsecs above the midplane. We find ionizing
fluxes throughout our simulation grids are larger than predicted by one
dimensional slab models, thus allowing for photoionization by O stars of low
altitude neutral clouds in the Galaxy that are also detected in Halpha. In
previous studies of such clouds the photoionization scenario had been rejected
and the Halpha had been attributed to enhanced cosmic ray ionization or
scattered light from midplane H II regions. We do find that the emission
measure distributions in our simulations are wider than those derived from
Halpha observations in the Milky Way. In addition, the horizontally averaged
height dependence of the gas density in the hydrodynamical models is lower than
inferred in the Galaxy. These discrepancies are likely due to the absence of
magnetic fields in the hydrodynamic simulations and we discuss how
magnetohydrodynamic effects may reconcile models and observations.
Nevertheless, we anticipate that the inclusion of magnetic fields in the
dynamical simulations will not alter our primary finding that midplane OB stars
are capable of producing high altitude diffuse ionized gas in a realistic
three-dimensional interstellar medium.Comment: ApJ accepted. 17 pages, 7 figure
Dependence of Interstellar Turbulent Pressure on Supernova Rate
Feedback from massive stars is one of the least understood aspects of galaxy
formation. We perform a suite of vertically stratified local interstellar
medium (ISM) simulations in which supernova rates and vertical gas column
densities are systematically varied based on the Schmidt-Kennicutt law. Our
simulations have a sufficiently high spatial resolution (1.95 pc) to follow the
hydrodynamic interactions among multiple supernovae that structure the ISM. At
a given supernova rate, we find that the mean mass-weighted sound speed and
velocity dispersion decrease as the inverse square root of gas density,
indicating that both thermal and turbulent pressures are nearly constant in the
midplane, so the effective equation of state is isobaric. In contrast, across
our four models having supernova rates that range from one to 512 times the
Galactic supernova rate, the mass-weighted velocity dispersion remains in the
range 4-6 km/s. Hence, gas averaged over ~100 pc regions follows an effective
equation of state that is close to isothermal. Simulated H I emission lines
have widths of 10-18 km/s, comparable to observed values. In our highest
supernova rate model, superbubble blow-outs occur, and the turbulent pressure
on large scales is >~4 times higher than the thermal pressure. We find a tight
correlation between the thermal and turbulent pressures averaged over ~100 pc
regions in the midplane of each model, as well as across the four ISM models.
We construct a subgrid model for turbulent pressure based on analytic arguments
and explicitly calibrate it against our stratified ISM simulations. The subgrid
model provides a simple yet physically motivated way to include supernova
feedback in cosmological simulations.Comment: 13 pages incl. 8 figures; accepted for publication in ApJ; contains a
new model of starburst galaxy showing superbubble blow-ou
Vertical structure of a supernova-driven turbulent magnetized ISM
Stellar feedback drives the circulation of matter from the disk to the halo
of galaxies. We perform three-dimensional magnetohydrodynamic simulations of a
vertical column of the interstellar medium with initial conditions typical of
the solar circle in which supernovae drive turbulence and determine the
vertical stratification of the medium. The simulations were run using a stable,
positivity-preserving scheme for ideal MHD implemented in the FLASH code. We
find that the majority (\approx 90 %) of the mass is contained in
thermally-stable temperature regimes of cold molecular and atomic gas at T <
200 K or warm atomic and ionized gas at 5000 K < T < 10^{4.2} K, with strong
peaks in probability distribution functions of temperature in both the cold and
warm regimes. The 200 - 10^{4.2} K gas fills 50-60 % of the volume near the
plane, with hotter gas associated with supernova remnants (30-40 %) and cold
clouds (< 10 %) embedded within. At |z| ~ 1-2 kpc, transition-temperature (10^5
K) gas accounts for most of the mass and volume, while hot gas dominates at |z|
> 3 kpc. The magnetic field in our models has no significant impact on the
scale heights of gas in each temperature regime; the magnetic tension force is
approximately equal to and opposite the magnetic pressure, so the addition of
the field does not significantly affect the vertical support of the gas. The
addition of a magnetic field does reduce the fraction of gas in the cold (< 200
K) regime with a corresponding increase in the fraction of warm (~ 10^4 K) gas.
However, our models lack rotational shear and thus have no large-scale dynamo,
which reduces the role of the field in the models compared to reality. The
supernovae drive oscillations in the vertical distribution of halo gas, with
the period of the oscillations ranging from ~ 30 Myr in the T < 200 K gas to ~
100 Myr in the 10^6 K gas, in line with predictions by Walters & Cox.Comment: Accepted for publication in ApJ. Replacement corrects an error in the
observed CNM pressure distribution in Figure 15 and associated discussio
Assessing risk for HIV infection among adolescent girls in South Africa: an evaluation of the VOICE risk score (HPTN 068)
INTRODUCTION: To maximize impact and minimize costs, antiretroviral pre-exposure prophylaxis (PrEP) interventions should be offered to those at highest risk for HIV infection. The risk score derived from the VOICE trial is one tool currently being utilized to determine eligibility in adolescent PrEP trials in sub-Saharan Africa. This study is aimed at evaluating the utility of the risk score in predicting HIV incidence among a cohort of adolescent girls in rural South Africa.
METHODS: We utilized data from HIV Prevention Trials Network (HPTN) 068, a phase III randomized controlled trial conducted in rural Mpumalanga province, South Africa. School-attending young women aged 13 to 20 years were enrolled into the trial from 2011 to 2012 and followed for up to three years. A risk score based on individual-level risk factors measured at enrolment was calculated for HPTN 068 participants who completed a one-year follow-up visit and were HIV seronegative at enrolment. Possible scores ranged from 0 to 10. A proportional hazards model was then used to determine if risk score at enrolment was predictive of incident HIV infection at follow-up and an area under the curve analysis was used to examine the predictive ability of the score.
RESULTS AND DISCUSSION: The risk score had limited variability in the HPTN 068 sample. Scores â„5 identified 85% of incident infections from 94% of the sample, compared to the VOICE sample in which scores â„5 identified 91% of incident infections from only 64% of participants. The risk score did not predict HIV incidence after one year of follow-up (hazard ratio = 1.029; 95% confidence interval (CI): 0.704, 1.503, p = .884) and showed poor predictive ability (area under the curve = 0.55; 95% CI: 0.44, 0.65). Certain individual risk factors that comprise the risk score may be context specific or not relevant for adolescent populations. Additional factors should be considered when assessing risk for the purposes of determining PrEP eligibility.
CONCLUSIONS: The VOICE risk score demonstrated low utility to predict HIV incidence in the HPTN 068 sample. Findings highlight the need for an age and developmentally appropriate tool for assessing risk for HIV infection among adolescents. Use of the VOICE risk score for determining PrEP eligibility in younger populations should be carefully considered
Type-Ia Supernova-driven Galactic Bulge Wind
Stellar feedback in galactic bulges plays an essential role in shaping the
evolution of galaxies. To quantify this role and facilitate comparisons with
X-ray observations, we conduct 3D hydrodynamical simulations with the adaptive
mesh refinement code, FLASH, to investigate the physical properties of hot gas
inside a galactic bulge, similar to that of our Galaxy or M31. We assume that
the dynamical and thermal properties of the hot gas are dominated by mechanical
energy input from SNe, primarily Type Ia, and mass injection from evolved stars
as well as iron enrichment from SNe. We study the bulge-wide outflow as well as
the SN heating on scales down to ~4 pc. An embedding scheme that is devised to
plant individual SNR seeds, allows to examine, for the first time, the effect
of sporadic SNe on the density, temperature, and iron ejecta distribution of
the hot gas as well as the resultant X-ray morphology and spectrum. We find
that the SNe produce a bulge wind with highly filamentary density structures
and patchy ejecta. Compared with a 1D spherical wind model, the non-uniformity
of simulated gas density, temperature, and metallicity substantially alters the
spectral shape and increases the diffuse X-ray luminosity. The differential
emission measure as a function of temperature of the simulated gas exhibits a
log-normal distribution, with a peak value much lower than that of the
corresponding 1D model. The bulk of the X-ray emission comes from the
relatively low temperature and low abundance gas shells associated with SN
blastwaves. SN ejecta are not well mixed with the ambient medium, at least in
the bulge region. These results, at least partly, account for the apparent lack
of evidence for iron enrichment in the soft X-ray-emitting gas in galactic
bulges and intermediate-mass elliptical galaxies.[...]Comment: 37 pages, 19 figures, submitted to MNRAS; comments are welcom
Chondrule Formation and Protoplanetary Disk Heating by Current Sheets in Non-Ideal Magnetohydrodynamic Turbulence
We study magnetic field steepening due to ambipolar diffusion (Brandenburg &
Zweibel 1994) in protoplanetary disk environments and draw the following
conclusions. Current sheets are generated in magnetically active regions of the
disk where the ionization fraction is high enough for the magnetorotational
instability to operate. In late stages of solar nebula evolution, the surface
density is expected to have lowered and dust grains to have gravitationally
settled to the midplane. If the local dust-to-gas mass ratio near the midplane
is increased above cosmic abundances by factors > 10^3, current sheets reach
high enough temperatures to melt millimeter-sized dust grains, and hence may
provide the mechanism to form meteoritic chondrules. In addition, these current
sheets possibly explain the near-infrared excesses observed in spectral energy
distributions (SEDs) of young stellar objects. Direct imaging of protoplanetary
disks via a nulling interferometer or, in the future, a multi-band, adaptive
optics coronagraph can test this hypothesis.Comment: 11 pages, 4 figures, submitted to Ap
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