173 research outputs found
educationUndergraduate: Journal of undergraduate research in education (Volume 8)
Edited by Tracy Jeffery and Daphne Whiteoak.
Contents:
'What are Practitionersâ Perceptions of Qualifications and Progression within the Early Yearsâ Sector? A Small Scale Research Project Within a Pre-School Setting' by Philippa Coldicott; 'The Benefits of Forest School to Children Aged 2-16: A Systematic Review' by Rebecca Dix; 'Slither Down the Snake of Success: The Link between Synthetic Phonics and Reading Attainment' by Kate Kent; 'Is the App Evaluation Rubric Developed by Weng and Taber-Doughty (2015) an Effective System for Educators to Select the Most Appropriate Apps for Children with Special Educational Needs in the United Kingdom?' by Alex Liddle; 'What do Upper KS2 Children from a Small Village Primary School Perceive to be the Benefits and Potential Challenges of Physical Education Lessons?' by Joseph Piper; 'Has Growing Awareness of Mental Health Issues been Reflected in Improvements in Support and Awareness Within Schools?' by Emily Spalding
The Radio Lifetime of Supernova Remnants and the Distribution of Pulsar Velocities at Birth
We have made VLA images of the fields around three young pulsars which have
resulted in the discovery of two new supernova remnants and confirmation of a
third. We argue that, in at least two cases and perhaps the third, the pulsars
are physically associated with these supernova remnants. A review of all known
young pulsars shows that the majority are associated with supernova remnants.
We show that the typical density of the interstellar medium into which the
supernova remnants are evolving has a density of 0.2 cm instead of the
low value of 0.01 cm which had been calculated from other studies, and
results in a considerably longer radio lifetime for supernova remnants. Both
the morphology of the supernova remnants and the location of the pulsars imply
that most of these young pulsars are born with large transverse velocities
(500 km s). This high velocity mean in the distribution of pulsar
velocities appears to be a general property of the pulsar population at birth,
not seen in proper motion studies, due to selection effects. We explore the
implications of this result as it relates to the origin of these velocities and
the galactic distribution of pulsars. High velocity pulsars can escape their
supernova remnant in a very short timescale, comparable to the lifetime of the
remnant and may even play a role in extending the observable radio lifetime of
the remnant. A significant fraction will be capable of escaping the disk of the
Galaxy, producing an extended halo population.Comment: (apJ accepted). uuencoded, compressed postscript file. 23 pages.
Hardcopies of figures and table available on request from [email protected]
Resolving the compact HII regions in N160A with HST
Using high-resolution imaging with the Hubble Space Telescope, we study the
Large Magellanic Cloud HII region N160A and uncover several striking features
of this complex massive star-forming site. The two compact high excitation HII
blobs (HEBs) A1 and A2 are for the first time resolved and their stellar
content and morphology is revealed. A1, being of higher excitation, is powered
by a single massive star whose strong wind has created a surrounding bubble. A2
harbors several exciting stars enshrouded inside large quantities of dust. The
whole N160A nebula is energized by three star clusters for which we obtain
photometry and study their color-magnitude diagram. The HII region is
particularly dusty, with extinction values reaching an A_v~2.5 mag in the
visible, and it is separated from the molecular cloud by an outstanding
ionization front. A previously detected infrared young stellar object is also
accurately located with respect to the HII region.Comment: 11 pages, 5 figures. Accepted for publication in Astronomy &
Astrophysics. A version of the paper with higher quality images is available
at http://wwwusr.obspm.fr/~heydari/projects/N16
The Circumnuclear Molecular Gas in the Seyfert Galaxy NGC4945
We have mapped the central region of NGC 4945 in the transition of
CO, CO, and CO, as well as the continuum at 1.3 mm, at an
angular resolution of 5\farc \times 3\farc with the Submillimeter Array. The
relative proximity of NGC 4945 (distance of only 3.8 Mpc) permits a detailed
study of the circumnuclear molecular gas and dust in a galaxy exhibiting both
an AGN (classified as a Seyfert 2) and a circumnuclear starburst in an inclined
ring with radius 2\farcs5 (50 pc). We find that all three molecular
lines trace an inclined rotating disk with major axis aligned with that of the
starburst ring and large-scale galactic disk, and which exhibits solid-body
rotation within a radius of 5\farc (95 pc). We infer an inclination
for the nuclear disk of , somewhat smaller than the
inclination of the large-scale galactic disk of . The
continuum emission at 1.3 mm also extends beyond the starburst ring, and is
dominated by thermal emission from dust. If it traces the same dust emitting in
the far-infrared, then the bulk of this dust must be heated by star-formation
activity rather than the AGN. We discover a kinematically-decoupled component
at the center of the disk with a radius smaller than 1\farcs4 (27 pc), but
which spans approximately the same range of velocities as the surrounding disk.
This component has a higher density than its surroundings, and is a promising
candidate for the circumnuclear molecular torus invoked by AGN unification
models.Comment: 13 pages, 10 figures,accepted by Ap
Dense gas in nearby galaxies XVI. The nuclear starburst environment in NGC4945
A multi-line millimeter-wave study of the nearby starburst galaxy NGC 4945
has been carried out using the Swedish-ESO Submillimeter Telescope (SEST). The
study covers the frequency range from 82 GHz to 354 GHz and includes 80
transitions of 19 molecules. 1.3 mm continuum data of the nuclear source are
also presented. A large number of molecular species indicate the presence of a
prominent high density interstellar gas component characterized by cm. Abundances of molecular species are calculated and
compared with abundances observed toward the starburst galaxies NGC 253 and M
82 and galactic sources. Apparent is an `overabundance' of HNC in the nuclear
environment of NGC 4945. While the HNC/HCN =1--0 line intensity ratio is
0.5, the HNC/HCN abundance ratio is 1. While HCN is subthermally
excited (8 K), CN is even less excited (3--4
K), indicating that it arises from a less dense gas component and that its
=2--1 line can be optically thin even though its =1--0 emission is
moderately optically thick. Overall, fractional abundances of NGC 4945 suggest
that the starburst has reached a stage of evolution that is intermediate
between those observed in NGC 253 and M 82. Carbon, nitrogen, oxygen and sulfur
isotope ratios are also determined. Within the limits of uncertainty, carbon
and oxygen isotope ratios appear to be the same in the nuclear regions of NGC
4945 and NGC 253. High O/O, low O/O and
N/N and perhaps also low S/S ratios appear to be
characteristic properties of a starburst environment in which massive stars
have had sufficient time to affect the isotopic composition of the surrounding
interstellar medium.Comment: 26 pages, 16 figures, accepted bt A&
The Molonglo Galactic Plane Survey: I. Overview and Images
The first epoch Molonglo Galactic Plane Survey (MGPS1) is a radio continuum
survey made using the Molonglo Observatory Synthesis Telescope (MOST) at 843
MHz with a resolution of 43" X 43" cosec |delta|. The region surveyed is 245
deg < l < 355 deg, |b| < 1.5 deg. The thirteen 9 deg X 3 deg mosaic images
presented here are the superposition of over 450 complete synthesis
observations, each taking 12 h and covering 70' X 70' cosec |delta|. The
root-mean-square sensitivity over much of the mosaiced survey is 1-2 mJy/beam
(1 sigma), and the positional accuracy is approximately 1" X 1" cosec |delta|
for sources brighter than 20 mJy. The dynamic range is no better than 250:1,
and this also constrains the sensitivity in some parts of the images. The
survey area of 330 sq deg contains well over 12,000 unresolved or barely
resolved objects, almost all of which are extra-galactic sources lying in the
Zone of Avoidance. In addition a significant fraction of this area is covered
by extended, diffuse emission associated with thermal complexes, discrete H II
regions, supernova remnants, and other structures in the Galactic interstellar
medium.Comment: Paper with 3 figures and 1 table + Table 2 + 7 jpg grayscales for Fig
4. Astrophysical Journal Supplement (in press) see also
http://www.astrop.physics.usyd.edu.au/MGP
Detection of 6.7 GHz methanol absorption towards hot corinos
Methanol masers at 6.7 GHz have been found exclusively towards high-mass star
forming regions. Recently, some Class 0 protostars have been found to display
conditions similar to what are found in hot cores that are associated with
massive star formation. These hot corino sources have densities, gas
temperatures, and methanol abundances that are adequate for exciting strong 6.7
GHz maser emission. This raises the question of whether 6.7 GHz methanol masers
can be found in both hot corinos and massive star forming regions, and if not,
whether thermal methanol emission can be detected. We searched for the 6.7 GHz
methanol line towards five hot corino sources in the Perseus region using the
Arecibo radio telescope. To constrain the excitation conditions of methanol, we
observed thermal submillimeter lines of methanol in the NGC1333-IRAS 4 region
with the APEX telescope. We did not detect 6.7 GHz emission in any of the
sources, but found absorption against the cosmic microwave background in
NGC1333-IRAS 4A and NGC1333-IRAS 4B. Using a large velocity gradient analysis,
we modeled the excitation of methanol over a wide range of physical parameters,
and verify that the 6.7 GHz line is indeed strongly anti-inverted for densities
lower than 10^6 cm^-3. We used the submillimeter observations of methanol to
verify the predictions of our model for IRAS 4A by comparison with other CH3OH
transitions. Our results indicate that the methanol observations from the APEX
and Arecibo telescopes are consistent with dense (n ~ 10^6 cm^-3), cold (T ~
15-30 K) gas. The lack of maser emission in hot corinos and low-mass
protostellar objects in general may be due to densities that are much higher
than the quenching density in the region where the radiation field is conducive
to maser pumping.Comment: Accepted by A&
Supernova Remnant Evolution in Wind Bubbles: A Closer Look at Kes 27
Massive Stars (> 8 solar masses) lose mass in the form of strong winds. These
winds accumulate around the star, forming wind-blown bubbles. When the star
explodes as a supernova (SN), the resulting shock wave expands within this
wind-blown bubble, rather than the interstellar medium. The properties of the
resulting remnant, its dynamics and kinematics, the morphology, and the
resulting evolution, are shaped by the structure and properties of the
wind-blown bubble. In this article we focus on Kes 27, a supernova remnant
(SNR) that has been proposed by Chen et al (2008) to be evolving in a
wind-blown bubble, explore its properties, and investigate whether the
properties could be ascribed to evolution of a SNR in a wind-blown bubble. Our
initial model does not support this conclusion, due to the fact that the
reflected shock is expanding into much lower densities.Comment: 5 pages, 3 figures. Revised version submitted to High Energy Density
Physics. To be published in a special issue of the proceedings of the 2012
HEDLA conferenc
How to win friends and influence people: the value of the cohort in a doctoral research training programme
open access articleThis article is not about retention and attrition rates, or about
successful outcomes, or about supervision, even though these are at
the nub of most research on the doctoral experience. This article
concerns the experiences of doctoral students undertaking educational
research methods training, as opposed to the experiences of the PhD
itself. The specific phenomenon identified in this small group study is
the value of peer interaction within the cohort. Three strands of this
relationship, namely peer support, cultural mix and bonding/ad-hoc
social gatherings have been investigated. Our findings illustrate the
importance and unexpected value of the âcohortâ on the participants in
this study as they journey towards academia
Radio Emission from the Composite Supernova Remnant G326.3-1.8 (MSH15-56)
High resolution radio observations of the composite supernova remnant (SNR)
G326.3-1.8 or MSH 15-56 with the Australia Telescope Compact Array show details
of both the shell and the bright plerion which is offset about 1/3 of the
distance from the center of the SNR to the shell. The shell appears to be
composed of thin filaments, typical of older shell SNRs. The central part of
the elongated plerion is composed of a bundle of parallel ridges which bulge
out at the ends and form a distinct ring structure on the northwestern end. The
magnetic field with a strength of order 45 microGauss, is directed along the
axis of the ridges but circles around the northwestern ring. This plerion is
large and bright in the radio but is not detected in x-ray or optical
wavelengths. There is, however, a faint hard x-ray feature closer to the shell
outside the plerion. Perhaps if the supernova explosion left a rapidly moving
magnetar with large energy input but initially rapid decay of both relativistic
particles and magnetic field, the observed differences with wavelength could be
explained.Comment: 15 pages, 10 figures, accepted by Ap
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