1,714 research outputs found
The status of the crown-of-thorns starfish (Acanthaster planci) in the Great Barrier Reef, Australia, assessed from the sediment record of John Brewer, Green Island and Heron Island reefs
[Extract from 1988 report] Over the last 30 years the crown-of-thorns starfish (Acanthaster planci) has caused extensive damage to many reefs in the Great Barrier Reef Province. John Brewer Reef and Green Island Reef are among those worst affected by A. planci predation during this period. Surface sediment from these two reefs was exhaustively picked for A. planci skeletal elements and found to be greatly enhanced in element abundance when compared to that of Heron Island Reef which has historically maintained very low-density starfish populations. Carbon-14 accelerator mass spectrometry (AMS) dating indicates that skeletal elements from the surface sediment of John Brewer and Green Island Reefs are of contemporary age. Core sampling shows that subsurface sediment at John Brewer and Green Island Reefs contains A. planci element densities comparable to those found in the surface sediment at these localities. Physical and biological reworking of elements within the sediment precludes the recognition of individual outbreaks in core stratigraphy. AMS element dates and bulk sediment dates, obtained by conventional Carbon-14 radiometry, show that subsurface elements are generally prehistoric and conform to an age structure preserved in the sediment pile. Assessed on a time-averaged basis, the density and distribution of subsurface elements suggest that A. planci outbreaks are not a recent phenomenon, but have been an integral part of the ecosystem for at least 7,000 years on John Brewer Reef and 3,000 years on Green Island Reef
An assessment of key risk factors for surgical site infection in patients undergoing surgery for spinal metastases
Objectives
This study aimed to determine the rate of surgical site infection (SSI) in patients undergoing surgery for spinal metastases, and identify key risk factors for SSI among this patient group.
Methods
A retrospective case note review was undertaken in 152 adult patients being treated at a single specialist centre for spinal surgery.
Results
Overall SSI rate was 11.2% per patients (9.7% per procedure). An increase in the risk of SSI was
observed when surgery involved a greater number of vertebral levels (odds ratio 1.26, P=0.019) when controlling for primary spinal region. Controlling for the number of spinal levels, the odds of SSI increased by a factor of 5.6 (P=0.103) when the primary surgical region was thoracic, as opposed
to cervical or lumbar.
Conclusions
In conclusion, surgery associated with multiple vertebral levels for treatment of spinal metastases,
particularly of the thoracic spine, is associated with increased risk of SSI
Minke whales change their swimming behavior with respect to their calling behavior, nearby conspecifics, and the environment in the central North Pacific
This research was supported by the Office of Naval Research (Code 322, Award Number N0001422WX01263), Commander, U.S. Pacific Fleet (Code N465JR, Award Number N0007023WR0EP8F), and tool development necessary for this analysis was supported by the U.S. Navy’s Living Marine Resources Program (Award Number N0002520WR0141R). AcknowledgmentsBehavioral responses to sonar have been observed in a number of baleen whales, including minke whales (Balaenoptera acutorostrata). Previous studies used acoustic minke whale boing detections to localize and track individual whales on the U.S. Pacific Missile Range Facility (PMRF) in Kaua ‘i, Hawai‘i before, during, and after Navy training activities. These analyses showed significant changes in central North Pacific minke whale distribution and swimming behavior during Navy sonar events. For the purposes of contextualizing changes in animal movement relative to Navy sonar, we expanded on this research to examine the natural variation in minke whale movement when Navy sonar was not present. This study included 2,245 acoustically derived minke whale tracks spanning the years 2012–2017 over all months that minke whales were detected (October–May). Minke whale movement was examined relative to calling season, day of the year, hour of day, wind speed, calling state (nominal or rapid), and distance to the nearest calling conspecific. Hidden Markov models were used to identify two kinematic states (slower, less directional movement and faster, more directional movement). The findings indicate that minke whales were more likely to travel in a faster and more directional state when they were calling rapidly, when other vocalizing minke whales were nearby, during certain times of the day and calling seasons, and in windier conditions, but these changes in movement were less intense than the changes observed during exposure to Navy sonar, when swim speeds were the fastest. These results start to put behavioral responses to Navy sonar into an environmental context to understand the severity of responses relative to natural changes in behavior.Publisher PDFPeer reviewe
Nonlinear analysis of a simple model of temperature evolution in a satellite
We analyse a simple model of the heat transfer to and from a small satellite
orbiting round a solar system planet. Our approach considers the satellite
isothermal, with external heat input from the environment and from internal
energy dissipation, and output to the environment as black-body radiation. The
resulting nonlinear ordinary differential equation for the satellite's
temperature is analysed by qualitative, perturbation and numerical methods,
which show that the temperature approaches a periodic pattern (attracting limit
cycle). This approach can occur in two ways, according to the values of the
parameters: (i) a slow decay towards the limit cycle over a time longer than
the period, or (ii) a fast decay towards the limit cycle over a time shorter
than the period. In the first case, an exactly soluble average equation is
valid. We discuss the consequences of our model for the thermal stability of
satellites.Comment: 13 pages, 4 figures (5 EPS files
Nonlinear analysis of spacecraft thermal models
We study the differential equations of lumped-parameter models of spacecraft
thermal control. Firstly, we consider a satellite model consisting of two
isothermal parts (nodes): an outer part that absorbs heat from the environment
as radiation of various types and radiates heat as a black-body, and an inner
part that just dissipates heat at a constant rate. The resulting system of two
nonlinear ordinary differential equations for the satellite's temperatures is
analyzed with various methods, which prove that the temperatures approach a
steady state if the heat input is constant, whereas they approach a limit cycle
if it varies periodically. Secondly, we generalize those methods to study a
many-node thermal model of a spacecraft: this model also has a stable steady
state under constant heat inputs that becomes a limit cycle if the inputs vary
periodically. Finally, we propose new numerical analyses of spacecraft thermal
models based on our results, to complement the analyses normally carried out
with commercial software packages.Comment: 29 pages, 4 figure
Density functional calculations for 4He droplets
A novel density functional, which accounts correctly for the equation of
state, the static response function and the phonon-roton dispersion in bulk
liquid helium, is used to predict static and dynamic properties of helium
droplets. The static density profile is found to exhibit significant
oscillations, which are accompanied by deviations of the evaporation energy
from a liquid drop behaviour in the case of small droplets. The connection
between such oscillations and the structure of the static response function in
the liquid is explicitly discussed. The energy and the wave function of excited
states are then calculated in the framework of time dependent density
functional theory. The new functional, which contains backflow-like effects, is
expected to yield quantitatively correct predictions for the excitation
spectrum also in the roton wave-length range.Comment: 15 pages, REVTEX, 10 figures available upon request or at
http://anubis.science.unitn.it/~dalfovo/papers/papers.htm
A fully integrated GIS-based model of particulate waste distribution from marine fish-cage sites
Modern Geographical Information System (GIS) offers a powerful modelling environment capable of handling large databases. It is a very suitable environment in which to develop a suite of tools designed for environmental management of aquaculture sites, including carrying capacity prediction, land–water interactions and multi-site effects. One such tool, presented here, is a fully integrated and validated particulate fish waste dispersion module which uses mass balance to estimate waste input and takes account of variable bathymetry and variable settling velocity for feed and faecal components. The model also incorporates the effect of cage movement on waste dispersion, the first such model to do so. When tidal range was low (1.67 m), the maximum movement of a 22 m diameter circular cage was 10.1 m and 7.7 m easting and northing, respectively. Highest deposition from particulate fish waste is under the cage and incorporation of cage movement increased the effective area under a cage by 72%. This reduced peak deposition measurements by up to 32% and reduced the average modelled feed and faecal settlement at the cage centre by 23% and 11%, respectively. The model was validated by comparing model predictions with observed deposition measured using sediment traps during three 2-week field trips at a fish farm on the west coast of Scotland. The mean ratio of observed to predicted waste deposition at 5–25 m from the cage centre ranged from 0.9 to 1.06, whilst under the cage the model over-predicts deposition (observed/predicted=2.21). Although far-field data was seen to be comparable the near-field discrepancies resulted in variable overall accuracy in the model. The overall accuracy based on August 2001 data was ±50.9%, on February 2002, ±72.8% and on April 2002, ±50.6%. Summarizing the data resulted in an overall average predictive accuracy of ±58.1%. © 2006 Elsevier B.V. All rights reserved
Active Amplification of the Terrestrial Albedo to Mitigate Climate Change: An Exploratory Study
This study explores the potential to enhance the reflectance of solar
insolation by the human settlement and grassland components of the Earth's
terrestrial surface as a climate change mitigation measure. Preliminary
estimates derived using a static radiative transfer model indicate that such
efforts could amplify the planetary albedo enough to offset the current global
annual average level of radiative forcing caused by anthropogenic greenhouse
gases by as much as 30 percent or 0.76 W/m2. Terrestrial albedo amplification
may thus extend, by about 25 years, the time available to advance the
development and use of low-emission energy conversion technologies which
ultimately remain essential to mitigate long-term climate change. However,
additional study is needed to confirm the estimates reported here and to assess
the economic and environmental impacts of active land-surface albedo
amplification as a climate change mitigation measure.Comment: 21 pages, 3 figures. In press with Mitigation and Adaptation
Strategies for Global Change, Springer, N
Robust Henderson III estimators of variance components in the nested error model
Common methods for estimating variance components in Linear Mixed Models include Maximum Likelihood (ML) and Restricted Maximum Likelihood (REML). These methods are based on the strong assumption of multivariate normal distribution and it is well know that they are very sensitive to outlying observations with respect to any of the random components. Several robust altematives of these methods have been proposed (e.g. Fellner 1986, Richardson and Welsh 1995). In this work we present several robust alternatives based on the Henderson method III which do not rely on the normality assumption and provide explicit solutions for the variance components estimators. These estimators can later be used to derive robust estimators of regression coefficients. Finally, we describe an application of this procedure to small area estimation, in which the main target is the estimation of the means of areas or domains when the within-area sample sizes are small
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