673 research outputs found
Effect of column base strength on steel portal frames in fire
In the UK, the design of steel portal frame buildings in fire is based on the Steel Construction Institute (SCI) design method, in which fire protection needs only be provided to the columns, provided that the column bases are designed to resist an overturning moment, M_OTM, calculated in accordance with the SCI design method. In this paper, a non-linear elastic-plastic implicit dynamic finite element model of a steel portal frame building in fire is described and used to assess the adequacy of the SCI design method. Both 2-D and 3-D models are used to analyse a building similar to the Exemplar frame described in the SCI design guide. Using the 2-D model, a parametric study comprising 27 frames is conducted. It is shown that the value of the overturning moment, calculated in accordance with the SCI design method, may not be sufficient to prevent collapse of the frame before 890 Ā°C
Effects of landmark distance and stability on accuracy of reward relocation
This work was supported by the University of St Andrews, the University of Lethbridge and the Natural Sciences and Engineering Council of Canada.Although small-scale navigation is well studied in a wide range of species, much of what is known about landmark use by vertebrates is based on laboratory experiments. To investigate how vertebrates in the wild use landmarks, we trained wild male rufous hummingbirds to feed from a flower that was placed in a constant spatial relationship with two artificial landmarks. In the first experiment, the landmarks and flower were 0.25, 0.5 or 1 m apart and we always moved them 3ā4 m after each visit by the bird. In the second experiment, the landmarks and flower were always 0.25 m apart and we moved them either 1 or 0.25 m between trials. In tests, in which we removed the flower, the hummingbirds stopped closer to the predicted flower location when the landmarks had been closer to the flower during training. However, while the distance that the birds stopped from the landmarks and predicted flower location was unaffected by the distance that the landmarks moved between trials, the birds directed their search nearer to the predicted direction of the flower, relative to the landmarks, when the landmarks and flower were more stable in the environment. In the field, then, landmarks alone were sufficient for the birds to determine the distance of a reward but not its direction.PostprintPostprintPeer reviewe
Wild rufous hummingbirds use local landmarks to return to rewarded locations
This work was supported by the University of St Andrews, the University of Lethbridge and the Natural Sciences and Engineering Council of Canada.Animals may remember an important location with reference to one or more visual landmarks. In the laboratory, birds and mammals often preferentially use landmarks near a goal (ālocal landmarksā) to return to that location at a later date. Although we know very little about how animals in the wild use landmarks to remember locations, mammals in the wild appear to prefer to use distant landmarks to return to rewarded locations. To examine what cues wild birds use when returning to a goal, we trained free-living hummingbirds to search for a reward at a location that was specified by three nearby visual landmarks. Following training we expanded the landmark array to test the extent that the birds relied on the local landmarks to return to the reward. During the test the hummingbirds' search was best explained by the birds having used the experimental landmarks to remember the reward location. How the birds used the landmarks was not clear and seemed to change over the course of each test. These wild hummingbirds, then, can learn locations in reference to nearby visual landmarks.PostprintPeer reviewe
Why study cognition in the wild (and how to test it)?
An animal's behavior is affected by its cognitive abilities, which are, in turn, a consequence of the environment in which an animal has evolved and developed. Although behavioral ecologists have been studying animals in their natural environment for several decades, over much the same period animal cognition has been studied almost exclusively in the laboratory. Traditionally, the study of animal cognition has been based on well-established paradigms used to investigate well-defined cognitive processes. This allows identification of what animals can do, but may not, however, always reflect what animals actually do in the wild. As both ecologists and some psychologists increasingly try to explain behaviors observable only in wild animals, we review the different motivations and methodologies used to study cognition in the wild and identify some of the challenges that accompany the combination of a naturalistic approach together with typical psychological testing paradigms. We think that studying animal cognition in the wild is likely to be most productive when the questions addressed correspond to the speciesā ecology and when laboratory cognitive tests are appropriately adapted for use in the field. Furthermore, recent methodological and technological advances will likely allow significant expansion of the species and questions that can be addressed in the wild.PostprintPostprintPeer reviewe
Inpatient use and area-level socio-environmental factors in people with psychosis
Purpose: There is consistent evidence that socio-environmental factors measured at an area-level, such as ethnic density, urban environment and deprivation are associated with psychosis risk. However, whether area-level socio-environmental factors are associated with outcomes following psychosis onset is less clear. This study aimed to examine whether the number of inpatient days used by people presenting to mental health services for psychosis was associated with five key area-level socio-environmental factors: deprivation, ethnic density, social capital, population density and social fragmentation. Methods: Using a historical cohort design based on electronic health records from the South London and Maudsley NHS Trust Foundation electronic Patient Journey System, people who presented for the first time to SLAM between 2007 and 2010 with psychosis were included. Structured data were extracted on age at presentation, gender, ethnicity, residential area at first presentation and number of inpatient days over 5 years of follow-up. Data on area-level socio-environmental factors taken from published sources were linked to participantsā residential addresses. The relationship between the number of inpatient days and each socio-environmental factor was investigated in univariate negative binomial regression models with time in contact with services treated as an offset variable. Results: A total of 2147 people had full data on area level outcomes and baseline demographics, thus, could be included in the full analysis. No area-level socio-environmental factors were associated with inpatient days. Conclusion: Although a robust association exists between socio-environmental factors and psychosis risk, in this study we found no evidence that neighbourhood deprivation was linked to future inpatient admissions following the onset of psychosis. Future work on the influence of area-level socio-environmental factors on outcome should examine more nuanced outcomes, e.g. recovery, symptom trajectory, and should account for key methodological challenges, e.g. accounting for changes in address
Classical Novae in the ASKAP Pilot Surveys
We present a systematic search for radio counterparts of novae using the
Australian Square Kilometer Array Pathfinder (ASKAP). Our search used the Rapid
ASKAP Continuum Survey, which covered the entire sky south of declination
( square degrees) at a central frequency of 887.5
MHz, the Variables and Slow Transients Pilot Survey, which covered
square degrees per epoch (887.5 MHz), and other ASKAP pilot surveys, which
covered square degrees with 2-12 hour integration times. We
crossmatched radio sources found in these surveys over a two-year period, from
April 2019 to August 2021, with 440 previously identified optical novae, and
found radio counterparts for four novae: V5668 Sgr, V1369 Cen, YZ Ret, and RR
Tel. Follow-up observations with the Australian Telescope Compact Array confirm
the ejecta thinning across all observed bands with spectral analysis indicative
of synchrotron emission in V1369 Cen and YZ Ret. Our light-curve fit with the
Hubble Flow model yields a value of
for the mass ejected in V1369 Cen. We also derive a peak surface brightness
temperature of K for YZ Ret. Using Hubble Flow model simulated radio
lightcurves for novae, we demonstrate that with a 5 sensitivity limit
of 1.5 mJy in 15-min survey observations, we can detect radio emission up to a
distance of 4 kpc if ejecta mass is in the range , and
upto 1 kpc if ejecta mass is in the range . Our
study highlights ASKAP's ability to contribute to future radio observations for
novae within a distance of 1 kpc hosted on white dwarfs with masses
, and within a distance of 4 kpc hosted on white dwarfs
with masses .Comment: This paper has been accepted for publication in PASA. It consists of
13 pages, 5 figures and 4 table
A pilot ASKAP survey for radio transients towards the Galactic Centre
We present the results of a radio transient and polarisation survey towards
the Galactic Centre, conducted as part of the Australian Square Kilometre Array
Pathfinder Variables and Slow Transients pilot survey. The survey region
consisted of five fields covering (, ). Each field was observed
for 12\,minutes, with between 7 and 9 repeats on cadences of between one day
and four months. We detected eight highly variable sources and seven highly
circularly-polarised sources (14 unique sources in total). Seven of these
sources are known pulsars including the rotating radio transient
PSR~J1739--2521 and the eclipsing pulsar PSR~J1723--2837. One of them is a low
mass X-ray binary, 4U 1758--25. Three of them are coincident with optical or
infrared sources and are likely to be stars. The remaining three may be related
to the class of Galactic Centre Radio Transients (including a highly likely
one, VAST~J173608.2--321634, that has been reported previously), although this
class is not yet understood. In the coming years, we expect to detect 40
bursts from this kind of source with the proposed four-year VAST survey if the
distribution of the source is isotropic over the Galactic fields.Comment: 17 pages, 13 figures, Accepted for publication in MNRA
Discovery of radio eclipses from 4FGL J1646.54406: a new candidate redback pulsar binary
Large widefield surveys make possible the serendipitous discovery of rare
sub-classes of pulsars. One such class are "spider"-type pulsar binaries,
comprised of a pulsar in a compact orbit with a low-mass (sub)stellar
companion. In a search for circularly-polarized radio sources in ASKAP Pilot
Survey observations, we discovered highly variable and circularly polarized
emission from a radio source within the error region of the -ray source
{4FGL}~J1646.54406. The variability is consistent with the eclipse of a
compact, steep-spectrum source behind ablated material from a companion in a
h binary orbit. Based on the eclipse properties and spatial
coincidence with {4FGL} J1646.54406, we argue that the source is likely a
recycled pulsar in a "redback" binary system. Using properties of the eclipses
from ASKAP and Murchison Widefield Array observations, we provide broad
constraints on the properties of the eclipse medium. We identified a potential
optical/infra-red counterpart in archival data consistent with a variable
low-mass star. Using the Parkes Radio Telescope "Murriyang" and MeerKAT, we
searched extensively for radio pulsations but yielded no viable detections of
pulsed emission. We suggest that the non-detection of pulses is due to
scattering in the intra-binary material, but scattering from the ISM can also
plausibly explain the pulse non-detections if the interstellar dispersion
measure exceeds 600pccm. Orbital constraints derived from
optical observations of the counterpart would be highly valuable for future
-ray pulsation searches, which may confirm the source nature as a
pulsar.Comment: Submitted to MNRAS. 13 Pages, 10 figures, 3 table
A search for radio afterglows from gamma-ray bursts with the Australian Square Kilometre Array Pathfinder
We present a search for radio afterglows from long gamma-ray bursts using the
Australian Square Kilometre Array Pathfinder (ASKAP). Our search used the Rapid
ASKAP Continuum Survey, covering the entire celestial sphere south of
declination , and three epochs of the Variables and Slow Transients
Pilot Survey (Phase 1), covering square degrees per epoch. The
observations we used from these surveys spanned a nine-month period from 2019
April 21 to 2020 January 11. We crossmatched radio sources found in these
surveys with 779 well-localised (to ) long gamma-ray bursts
occurring after 2004 and determined whether the associations were more likely
afterglow- or host-related through the analysis of optical images. In our
search, we detected one radio afterglow candidate associated with GRB 171205A,
a local low-luminosity gamma-ray burst with a supernova counterpart SN 2017iuk,
in an ASKAP observation 511 days post-burst. We confirmed this detection with
further observations of the radio afterglow using the Australia Telescope
Compact Array at 859 days and 884 days post-burst. Combining this data with
archival data from early-time radio observations, we showed the evolution of
the radio spectral energy distribution alone could reveal clear signatures of a
wind-like circumburst medium for the burst. Finally, we derived semi-analytical
estimates for the microphysical shock parameters of the burst: electron
power-law index , normalised wind-density parameter ,
fractional energy in electrons , and fractional energy in
magnetic fields .Comment: 18 pages, 7 figures; accepted for publication in MNRA
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