1,924 research outputs found
Stochastic perturbations in open chaotic systems: random versus noisy maps
We investigate the effects of random perturbations on fully chaotic open
systems. Perturbations can be applied to each trajectory independently (white
noise) or simultaneously to all trajectories (random map). We compare these two
scenarios by generalizing the theory of open chaotic systems and introducing a
time-dependent conditionally-map-invariant measure. For the same perturbation
strength we show that the escape rate of the random map is always larger than
that of the noisy map. In random maps we show that the escape rate and
dimensions of the relevant fractal sets often depend nonmonotonically on
the intensity of the random perturbation. We discuss the accuracy (bias) and
precision (variance) of finite-size estimators of and , and show
that the improvement of the precision of the estimations with the number of
trajectories is extremely slow (). We also argue that the
finite-size estimators are typically biased. General theoretical results
are combined with analytical calculations and numerical simulations in
area-preserving baker maps.Comment: 12 pages, 3 figures, 1 table, manuscript submitted to Physical Review
Noise-enhanced trapping in chaotic scattering
We show that noise enhances the trapping of trajectories in scattering
systems. In fully chaotic systems, the decay rate can decrease with increasing
noise due to a generic mismatch between the noiseless escape rate and the value
predicted by the Liouville measure of the exit set. In Hamiltonian systems with
mixed phase space we show that noise leads to a slower algebraic decay due to
trajectories performing a random walk inside Kolmogorov-Arnold-Moser islands.
We argue that these noise-enhanced trapping mechanisms exist in most scattering
systems and are likely to be dominant for small noise intensities, which is
confirmed through a detailed investigation in the Henon map. Our results can be
tested in fluid experiments, affect the fractal Weyl's law of quantum systems,
and modify the estimations of chemical reaction rates based on phase-space
transition state theory.Comment: 5 pages, 5 figure
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Prediction of long-term survival and coagulation factor VIII levels: interactions with gender in a large hospital-based cohort
Synthesis of niobium-alumina composite aggregates and their application in coarse-grained refractory ceramic-metal castables
Niobium-alumina aggregate fractions with particle sizes up to 3150 ”m were produced by crushing pre-synthesised fine-grained composites. Phase separation with niobium enrichment in the aggregate class 45â500 ”m was revealed by XRD/Rietveld analysis. To reduce the amount of carbon-based impurities, no organic additives were used for the castable mixtures, which resulted in water demands of approximately 27 vol.% for the fine- and coarse-grained castables. As a consequence, open porosities of 18% and 30% were determined for the fine- and coarse-grained composites, respectively. Due to increased porosity, the modulus of rupture at room temperature decreased from 52 MPa for the fine-grained composite to 11 MPa for the coarse-grained one. However, even the compressive yield strength decreased from 49 MPa to 18 MPa at 1300 °C for the fine-grained to the coarse-grained composite, the latter showed still plasticity with a strain up to 5%. The electrical conductivity of fine-grained composite samples was in the range between 40 and 60 S/cm, which is fifteen magnitudes above the values of pure corundum
Wireless Connectivity of a Ground-and-Air Sensor Network
This paper shows that, when considering outdoor scenarios and wireless
communications using the IEEE 802.11 protocol with dipole antennas, the ground
reflection is a significant propagation mechanism. This way, the Two-Ray model
for this environment allows predicting, with some accuracy, the received signal
power. This study is relevant for the application in the communication between
overflying Unmanned Aerial Vehicles (UAVs) and ground sensors. In the proposed
Wireless Sensor Network (WSN) scenario, the UAVs must receive information from
the environment, which is collected by sensors positioned on the ground, and
need to maintain connectivity between them and the base station, in order to
maintain the quality of service, while moving through the environment.Comment: 8 pages, 11 figure
Death feigning as an adaptive antiâpredator behaviour: Further evidence for its evolution from artificial selection and natural populations
Death feigning is considered to be an adaptive antipredator behaviour. Previous studies on Tribolium castaneum have shown that prey which death feign have a fitness advantage over those that do not when using a jumping spider as the predator. Whether these effects are repeatable across species or whether they can be seen in nature is, however, unknown. Therefore, the present study involved two experiments: (a) divergent artificial selection for the duration of death feigning using a related species T. freemani as prey and a predatory bug as predator, demonstrating that previous results are repeatable across both prey and predator species, and (b) comparison of the deathâfeigning duration of T. castaneum populations collected from field sites with and without predatory bugs. In the first experiment, T. freemani adults from established selection regimes with longer durations of death feigning had higher survival rates and longer latency to being preyed on when they were placed with predatory bugs than the adults from regimes selected for shorter durations of death feigning. As a result, the adaptive significance of deathâfeigning behaviour was demonstrated in another preyâpredator system. In the second experiment, wild T. castaneum beetles from populations with predators feigned death longer than wild beetles from predatorâfree populations. Combining the results from these two experiments with those from previous studies provided strong evidence that predators drive the evolution of longer death feigning
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