6,334 research outputs found
Design degrees of freedom and mechanisms for complexity
We develop a discrete spectrum of percolation forest fire models characterized by increasing design degrees of freedom (DDOF’s). The DDOF’s are tuned to optimize the yield of trees after a single spark. In the limit of a single DDOF, the model is tuned to the critical density. Additional DDOF’s allow for increasingly refined spatial patterns, associated with the cellular structures seen in highly optimized tolerance (HOT). The spectrum of models provides a clear illustration of the contrast between criticality and HOT, as well as a concrete quantitative example of how a sequence of robustness tradeoffs naturally arises when increasingly complex systems are developed through additional layers of design. Such tradeoffs are familiar in engineering and biology and are a central aspect of the complex systems that can be characterized as HOT
Thermoradiation inactivation of naturally occurring organisms in soil
Samples of soil collected from Kennedy Space Center near spacecraft assembly facilities were found to contain microorganisms very resistant to conventional sterilization techniques. The inactivation behavior of the naturally occurring spores in soil was investigated using dry heat and ionizing radiation, first separately, then in combination. Dry heat inactivation rates of spores were determined for 105 and 125 C. Radiation inactivation rates were determined for dose rates of 660 and 76 krad/hr at 25 C. Simultaneous combinations of heat and radiation were then investigated at 105, 110, 115, 120, and 125 C. Combined treatment was found to be highly synergistic requiring greatly reduced radiation doses to accomplish sterilization
The effect of within-crop habitat manipulations on the conservation biological control of aphids in field-grown lettuce
Within-crop habitat manipulations have the potential to increase the biological
control of pests in horticultural field crops. Wildflower strips have been shown to
increase the abundance of natural enemies, but there is little evidence to date of an
impact on pest populations. The aim of this study was to determine whether withincrop
wildflower strips can increase the natural regulation of pests in horticultural
field crops. Aphid numbers in plots of lettuce grown adjacent to wildflower strips
were compared with those in plots grown in the absence of wildflowers. The presence
of wildflower strips led to a decrease in aphid numbers on adjacent lettuce plants
during June and July, but had less impact in August and September. The decrease in
aphid numbers was greatest close to the wildflower strips and, the decrease in aphid
numbers declined with increasing distance from the wildflower strips, with little
effect at a distance of ten metres. The main natural enemies found in the crop were
those that dispersed aerially, which is consistent with data from previous studies on
cereal crops. Analysis and interpretation of natural enemy numbers was difficult due
to low recovery of natural enemies, and the numbers appeared to follow changes in
aphid abundance rather than being directly linked to the presence of wildflower
strips. Cutting the wildflower strips, to remove floral resources, had no impact on the
reduction in aphid numbers achieved during June and July, but decreased the effect
of the wildflower strips during August and September. The results suggest that
wildflower strips can lead to increased natural regulation of pest aphids in outdoor
lettuce crops, but more research is required to determine how this is mediated by
natural enemies and how the impact of wildflower strips on natural pest regulation
changes during the growing season
Photoionization of Galactic Halo Gas by Old Supernova Remnants
We present new calculations on the contribution from cooling hot gas to the
photoionization of warm ionized gas in the Galaxy. We show that hot gas in
cooling supernova remnants (SNRs) is an important source of photoionization,
particularly for gas in the halo. We find that in many regions at high latitude
this source is adequate to account for the observed ionization so there is no
need to find ways to transport stellar photons from the disk. The flux from
cooling SNRs sets a floor on the ionization along any line of sight. Our model
flux is also shown to be consistent with the diffuse soft X-ray background and
with soft X-ray observations of external galaxies.
We consider the ionization of the clouds observed towards the halo star HD
93521, for which there are no O stars close to the line of sight. We show that
the observed ionization can be explained successfully by our model EUV/soft
X-ray flux from cooling hot gas. In particular, we can match the H alpha
intensity, the S++/S+ ratio, and the C+* column. From observations of the
ratios of columns of C+* and either S+ or H0, we are able to estimate the
thermal pressure in the clouds. The slow clouds require high (~10^4 cm^-3 K)
thermal pressures to match the N(C+*)/N(S+) ratio. Additional heating sources
are required for the slow clouds to maintain their ~7000 K temperatures at
these pressures, as found by Reynolds, Hausen & Tufte (1999).Comment: AASTeX 5.01; 34 pages, 2 figures; submitted to Astrophysical Journa
Influence of the duration of a treadmill walking bout on heart rate variability at rest in physically active women
Background: Heart rate variability (HRV) has been promoted as a noninvasive method of evaluating autonomic influence on cardiac rhythm. Although female subjects predominate in the walking studies, no study to date has examined the influence of the duration of a moderate intensity walking physical activity bout on HRV in this population. Methods: Twelve healthy physically active middle-aged women undertook 2 conditions; 20min (W20) and 60min (W60) bouts of walking on a treadmill. Resting HRV measures were obtained before (-1 h), and 1 h and 24 h after the walking bouts. Results: Mean NN interval (ie, normal-to-normal intervals between adjacent QRS complexes) was significantly lower (P = .017) at +1 h in W60 (832, 686-979ms) compared with W20 (889, 732-1046ms). A borderline main effect for time was observed for both the SDNN intervals in W60 (P = .056), and for low frequency (LF(abs)) power in W60 (P = .047), with post hoc tests revealing a significant increase between 1 h (51, 33-69 ms and 847, 461-1556 ms(2)) and +1 h (65, 34-97ms and 1316, 569-3042 ms(2)) for SDNN and LF(abs) power, respectively, but no increase at +24h compared with -1 h. Conclusions: It appears that a walking bout of 60 min duration does alter cardiac autonomic influence in healthy active women, and this alteration is not evident after 20 min of walking. Given the rather subtle effect, further studies with larger sample sizes are required to explore the nature of the changes in cardiac autonomic influence following a prolonged bout of walking
Observations of X-rays and Thermal Dust Emission from the Supernova Remnant Kes 75
We present Spitzer Space Telescope and Chandra X-ray Observatory observations
of the composite Galactic supernova remnant Kes 75 (G29.7-0.3). We use the
detected flux at 24 microns and hot gas parameters from fitting spectra from
new, deep X-ray observations to constrain models of dust emission, obtaining a
dust-to-gas mass ratio M_dust/M_gas ~0.001. We find that a two-component
thermal model, nominally representing shocked swept-up interstellar or
circumstellar material and reverse-shocked ejecta, adequately fits the X-ray
spectrum, albeit with somewhat high implied densities for both components. We
surmise that this model implies a Wolf-Rayet progenitor for the remnant. We
also present infrared flux upper limits for the central pulsar wind nebula.Comment: 7 pages, 2 tables, 4 figures, uses emulateapj. Accepted for
publication in Ap
Sedation for Gastrointestinal Endoscopic Procedures in the Elderly: Getting Safer but Still Not Nearly Safe Enough
Previously published UK reports showed that excessively large doses of benzodiazepines and opiates were being commonly used to sedate elderly patients for gastrointestinal (GI) endoscopy. This unsafe practice has lead to avoidable morbidity and mortality. We have taken the opportunity provided by recent reports to examine whether GI endoscopy sedation practice in the elderly has improved in the light of this evidence and the publication of guidelines in which specific recommendations on sedation dosage are given
Series Intermittent Sand Filtration of Wastewater Lagoon Effluents
Previous researches have found single stage intermittent sand filtration to be a feasible and economic means of upgrading wastewater lagoon effluent to meet future standards. However the major constraint on their use has been the length of the filter runs. Laboratory scale and pilot-scale series intermittent sand filtration of wastewater lagoon effluents has been found to substantially increase the length of filter runs as well as produce a high quality effluent able to meet future standards. Higher loading rates were round to be possible with series intermittent sand filtration. The operation consistently produced an effluent meeting present Utah “Class C” water quality standards for BOD5 (\u3c5 mg/l), and the operation also consistently met the 1980 Utah wastewater treatment plant effluent standard for suspended solids (\u3c 10 mg/l)
Enabling GPU Accelerated Computing in the SUNDIALS Time Integration Library
As part of the Exascale Computing Project (ECP), a recent focus of
development efforts for the SUite of Nonlinear and DIfferential/ALgebraic
equation Solvers (SUNDIALS) has been to enable GPU-accelerated time integration
in scientific applications at extreme scales. This effort has resulted in
several new GPU-enabled implementations of core SUNDIALS data structures,
support for programming paradigms which are aware of the heterogeneous
architectures, and the introduction of utilities to provide new points of
flexibility. In this paper, we discuss our considerations, both internal and
external, when designing these new features and present the features
themselves. We also present performance results for several of the features on
the Summit supercomputer and early access hardware for the Frontier
supercomputer, which demonstrate negligible performance overhead resulting from
the additional infrastructure and significant speedups when using both NVIDIA
and AMD GPUs
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