3,729 research outputs found
VFR-into-IMC: An Analysis of Two Training Protocols on Weather-Related Posttest Scores
According to the Aircraft Owners and Pilots Association Air Safety Institute, 264 accidents were identified as continued visual flight rules (VFR) into instrument meteorological conditions (IMC), during the past ten years. Approximately 89% of those VFR-into-IMC accidents were fatal, causing hundreds of deaths. VFR-into-IMC has been a major concern for the general aviation community, prompting focused efforts. Research, data analyses, outreach, training, and education are recommended practices to address risks associated with VFR-into-IMC. Researchers of the current study sought to evaluate the cause and effect relationship between two training protocols and weather-related posttest scores. A pretest–posttest experimental design was utilized at two testing locations. Participants were randomly assigned to one of three groups: a control group, an interactive online training group, or an interactive workshop group. An analysis of covariance was used to determine whether there was a significant difference between mean posttest scores among the experimental groups while controlling for pretest scores. The treatments did not appear to significantly increase posttest scores after controlling for pretest scores, at either experiment location. Though the results of this study did not yield anticipated findings, much was learned and potentially helpful to general aviation researchers seeking to mitigate VFR-into-IMC encounters. Recommendations for future research and practices are discussed
The intervening role of urgency on the association between childhood maltreatment, PTSD, and substance-related problems
A range of risk factors lead to opioid use and substance-related problems (SRP) including childhood maltreatment, elevated impulsivity, and psychopathology. These constructs are highly interrelated such that childhood maltreatment is associated with elevated impulsivity and trauma-related psychopathology such as posttraumatic stress disorder (PTSD), and impulsivity-particularly urgency-and PTSD are related. Prior work has examined the association between these constructs and substance-related problems independently and it is unclear how these multi-faceted constructs (i.e., maltreatment types and positive and negative urgency) are associated with one another and SRP. The current study used structural equation modeling (SEM) to examine the relations among childhood maltreatment, trait urgency, PTSD symptoms, and SRP in a sample of individuals with a history of opioid use. An initial model that included paths from each type of childhood maltreatment, positive and negative urgency, PTSD and SRP did not fit the data well. A pruned model with excellent fit was identified that suggested emotional abuse, positive urgency, and negative urgency were directly related to PTSD symptoms and only PTSD symptoms were directly related to SRP. Furthermore, significant indirect effects suggested that emotional abuse and negative urgency were related to SRP via PTSD symptom severity. These results suggest that PTSD plays an important role in the severity of SRP
Reading aloud boosts connectivity through the putamen
Functional neuroimaging and lesion studies have frequently reported thalamic and putamen activation during reading and speech production. However, it is currently unknown how activity in these structures interacts with that in other reading and speech production areas. This study investigates how reading aloud modulates the neuronal interactions between visual recognition and articulatory areas, when both the putamen and thalamus are explicitly included. Using dynamic causal modeling in skilled readers who were reading regularly spelled English words, we compared 27 possible pathways that might connect the ventral anterior occipito-temporal sulcus (aOT) to articulatory areas in the precentral cortex (PrC). We focused on whether the neuronal interactions within these pathways were increased by reading relative to picture naming and other visual and articulatory control conditions. The results provide strong evidence that reading boosts the aOT–PrC pathway via the putamen but not the thalamus. However, the putamen pathway was not exclusive because there was also evidence for another reading pathway that did not involve either the putamen or the thalamus. We conclude that the putamen plays a special role in reading but this is likely to vary with individual reading preferences and strategies
Radiative Falloff in Neutron Star Spacetimes
We systematically study late-time tails of scalar waves propagating in
neutron star spacetimes. We consider uniform density neutron stars, for which
the background spacetime is analytic and the compaction of the star can be
varied continously between the Newtonian limit 2M/R << 1 and the relativistic
Buchdahl limit 2M/R = 8/9. We study the reflection of a finite wave packet off
neutron stars of different compactions 2M/R and find that a Newtonian, an
intermediate, and a highly relativistic regime can be clearly distinguished. In
the highly relativistic regime, the reflected signal is dominated by
quasi-periodic peaks, which originate from the wave packet bouncing back and
forth between the center of the star and the maximum of the background
curvature potential at R ~ 3 M. Between these peaks, the field decays according
to a power-law. In the Buchdahl limit 2M/R -> 8/9 the light travel time between
the center and the maximum or the curvature potential grows without bound, so
that the first peak arrives only at infinitely late time. The modes of neutron
stars can therefore no longer be excited in the ultra-relativistic limit, and
it is in this sense that the late-time radiative decay from neutron stars
looses all its features and gives rise to power-law tails reminiscent of
Schwarzschild black holes.Comment: 10 pages, 7 figures, to appear in PR
Why are most molecular clouds not gravitationally bound?
The most recent observational evidence seems to indicate that giant molecular
clouds are predominantly gravitationally unbound objects. In this paper we show
that this is a natural consequence of a scenario in which cloud-cloud
collisions and stellar feedback regulate the internal velocity dispersion of
the gas, and so prevent global gravitational forces from becoming dominant.
Thus, while the molecular gas is for the most part gravitationally unbound,
local regions within the denser parts of the gas (within the clouds) do become
bound and are able to form stars. We find that the observations, in terms of
distributions of virial parameters and cloud structures, can be well modelled
provided that the star formation efficiency in these bound regions is of order
5 - 10 percent. We also find that in this picture the constituent gas of
individual molecular clouds changes over relatively short time scales,
typically a few Myr.Comment: 9 pages, 8 figures, accepted for publication in MNRA
Long Term Implications of Climate Change on Crop Planning
The effects of climate change have been much speculated on in the past few years. Consequently, there has been intense interest in one of its key issues of food security into the future. This is particularly so given population increase, urban encroachment on arable land, and the degradation of the land itself. Recently, work has been done on predicting precipitation and temperature for the next few decades as well as developing optimisation models for crop planning. Combining these together, this paper examines the effects of climate change on a large food producing region in Australia, the Murrumbidgee Irrigation Area. For time periods between 1991 and 2071 for dry, average and wet years, an analysis is made about the way that crop mixes will need to change to adapt for the effects of climate change. It is found that sustainable crop choices will change into the future, and that large-scale irrigated agriculture may become unviable in the region in all but the wettest years
Radiation tails and boundary conditions for black hole evolutions
In numerical computations of Einstein's equations for black hole spacetimes,
it will be necessary to use approximate boundary conditions at a finite
distance from the holes. We point out here that ``tails,'' the inverse
power-law decrease of late-time fields, cannot be expected for such
computations. We present computational demonstrations and discussions of
features of late-time behavior in an evolution with a boundary condition.Comment: submitted to Phys. Rev.
The ISM in spiral galaxies: can cooling in spiral shocks produce molecular clouds?
We investigate the thermodynamics of the ISM and the formation of molecular
hydrogen through numerical simulations of spiral galaxies. The model follows
the chemical, thermal and dynamical response of the disc to an external spiral
potential. Self-gravity and magnetic fields are not included. The calculations
demonstrate that gas can cool rapidly when subject to a spiral shock. Molecular
clouds in the spiral arms arise through a combination of compression of the ISM
by the spiral shock and orbit crowding. These results highlight that local
self-gravity is not required to form molecular clouds. Self-shielding provides
a sharp transition density, below which gas is essentially atomic, and above
which the molecular gas fraction is >0.001. The timescale for gas to move
between these regimes is very rapid (<~1 Myr). From this stage, the majority of
gas generally takes between 10 to 20 Myr to obtain high H fractions (>50
%). Although our calculations are unable to resolve turbulent motions on scales
smaller than the spiral arm and do not include self-gravity. True cloud
formation timescales are therefore expected to be even shorter.
The mass budget of the disc is dominated by cold gas residing in the spiral
arms. Between 50 and 75 % of this gas is in the atomic phase. When this gas
leaves the spiral arm and drops below the self-shielding limit it is heated by
the galactic radiation field. Consequently, most of the volume in the interarm
regions is filled with warm atomic gas. However, some cold spurs and clumps can
survive in interarm regions for periods comparable to the interarm passage
timescale. Altogether between 7 and 40% of the gas in our disc is molecular,
depending on the surface density of the calculation, with approximately 20%
molecular for a surface density comparable to the solar neighbourhood.Comment: 16 pages, 19 figures, accepted for publication in MNRA
The efficiency of star formation in clustered and distributed regions
We investigate the formation of both clustered and distributed populations of
young stars in a single molecular cloud. We present a numerical simulation of a
10,000 solar mass elongated, turbulent, molecular cloud and the formation of
over 2500 stars. The stars form both in stellar clusters and in a distributed
mode which is determined by the local gravitational binding of the cloud. A
density gradient along the major axis of the cloud produces bound regions that
form stellar clusters and unbound regions that form a more distributed
population. The initial mass function also depends on the local gravitational
binding of the cloud with bound regions forming full IMFs whereas in the
unbound, distributed regions the stellar masses cluster around the local Jeans
mass and lack both the high-mass and the low-mass stars. The overall efficiency
of star formation is ~ 15 % in the cloud when the calculation is terminated,
but varies from less than 1 % in the the regions of distributed star formation
to ~ 40 % in regions containing large stellar clusters. Considering that large
scale surveys are likely to catch clouds at all evolutionary stages, estimates
of the (time-averaged) star formation efficiency for the giant molecular cloud
reported here is only ~ 4 %. This would lead to the erroneous conclusion of
'slow' star formation when in fact it is occurring on a dynamical timescale.Comment: 9 pages, 8 figures, MNRAS in pres
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