304 research outputs found
Balancing Selection Pressures, Multiple Objectives, and Neural Modularity to Coevolve Cooperative Agent Behavior
Previous research using evolutionary computation in Multi-Agent Systems
indicates that assigning fitness based on team vs.\ individual behavior has a
strong impact on the ability of evolved teams of artificial agents to exhibit
teamwork in challenging tasks. However, such research only made use of
single-objective evolution. In contrast, when a multiobjective evolutionary
algorithm is used, populations can be subject to individual-level objectives,
team-level objectives, or combinations of the two. This paper explores the
performance of cooperatively coevolved teams of agents controlled by artificial
neural networks subject to these types of objectives. Specifically, predator
agents are evolved to capture scripted prey agents in a torus-shaped grid
world. Because of the tension between individual and team behaviors, multiple
modes of behavior can be useful, and thus the effect of modular neural networks
is also explored. Results demonstrate that fitness rewarding individual
behavior is superior to fitness rewarding team behavior, despite being applied
to a cooperative task. However, the use of networks with multiple modules
allows predators to discover intelligent behavior, regardless of which type of
objectives are used
Global tide simulations with ICON-O: testing the model performance on highly irregular meshes
The global tide is simulated with the global ocean general circulation model ICON-O using a newly developed tidal module, which computes the full tidal potential. The simulated coastal M2 amplitudes, derived by a discrete Fourier transformation of the output sea level time series, are compared with the according values derived from satellite altimetry (TPXO-8 atlas). The experiments are repeated with four uniform and sixteen irregular triangular grids. The results show that the quality of the coastal tide simulation depends primarily on the coastal resolution and that the ocean interior can be resolved up to twenty times lower without causing considerable reductions in quality. The mesh transition zones between areas of different resolutions are formed by cell bisection and subsequent local spring optimisation tolerating a triangular cell’s maximum angle up to 84°. Numerical problems with these high-grade non-equiangular cells were not encountered. The results emphasise the numerical feasibility and potential efficiency of highly irregular computational meshes used by ICON-O. © 2020, The Author(s)
MAVERIC: A Data-Driven Approach to Personalized Autonomous Driving
Personalization of autonomous vehicles (AV) may significantly increase trust,
use, and acceptance. In particular, we hypothesize that the similarity of an
AV's driving style compared to the end-user's driving style will have a major
impact on end-user's willingness to use the AV. To investigate the impact of
driving style on user acceptance, we 1) develop a data-driven approach to
personalize driving style and 2) demonstrate that personalization significantly
impacts attitudes towards AVs. Our approach learns a high-level model that
tunes low-level controllers to ensure safe and personalized control of the AV.
The key to our approach is learning an informative, personalized embedding that
represents a user's driving style. Our framework is capable of calibrating the
level of aggression so as to optimize driving style based upon driver
preference. Across two human subject studies (n = 54), we first demonstrate our
approach mimics the driving styles of end-users and can tune attributes of
style (e.g., aggressiveness). Second, we investigate the factors (e.g., trust,
personality etc.) that impact homophily, i.e. an individual's preference for a
driving style similar to their own. We find that our approach generates driving
styles consistent with end-user styles (p<.001) and participants rate our
approach as more similar to their level of aggressiveness (p=.002). We find
that personality (p<.001), perceived similarity (p<.001), and high-velocity
driving style (p=.0031) significantly modulate the effect of homophily
Tidal impacts on primary production in the North Sea
This study highlights the importance of tides in controlling the spatial and
temporal distributions of phytoplankton and other factors related to growth,
such as nutrients and light availability. To quantify the responses of net
primary production (NPP) to tidal forcing, we conducted scenario model
simulations considering M2 and S2 tidal constituents using the
physical–biogeochemical coupled model ECOSMO (ECOSystem MOdel). The results were
analyzed with respect to a reference simulation without tidal forcing, with
particular focus on the spatial scale of the tidally induced changes. Tidal
forcing regulates the mixing–stratification processes in shelf seas such as
the North Sea and hence also influences ecosystem dynamics. In principle, the
results suggest three different response types with respect to primary
production: (i)Â in southern shallow areas with strong tidal energy
dissipation, tidal mixing dilutes phytoplankton concentrations in the upper
water layers and thereby decreases NPP. Additionally, tides increase
turbidity in near-coastal shallow areas, which has the potential to further
hamper NPP. (ii)Â In the frontal region of the southern North Sea, which is a
transition zone between stratified and mixed areas, tidal mixing infuses
nutrients into the surface mixed layer and resolves summer nutrient
depletion, thus sustaining the NPP during the summer season after spring
bloom nutrient depletion. (iii)Â In the northern North Sea, the NPP response
to tidal forcing is limited. Additionally, our simulations indicate that
spring bloom phenology is impacted by tidal forcing, leading to a later onset
of the spring bloom in large parts of the North Sea and to generally higher
spring bloom peak phytoplankton biomasses. By testing the related changes in
stratification, light conditions and grazing pressure, we found that all
three factors potentially contribute to the change in spring bloom phenology
with clear local differences. Finally, we also analyzed the impact of the
spring–neap tidal cycle on NPP. The annual mean impact of spring–neap tidal
forcing on NPP is limited. However, locally, we found substantial differences
in NPP either in phase or anti-phase with the spring–neap tidal cycle. These
differences could be attributed to locally different dominant factors such as
light or nutrient availability during spring tides. In general, we conclude
that in shallow shelf seas such as the North Sea, intensified vertical mixing
induced by tidal forcing could either promote NPP by counteracting nutrient
depletion or hinder NPP by deteriorating the light environment because of the
resuspension and mixing of suspended matter into the euphotic zone.</p
Compound flood events: analysing the joint occurrence of extreme river discharge events and storm surges in northern and central Europe
The simultaneous occurrence of extreme events gained more and more attention from scientific research in the last couple of years.
Compared to the occurrence of single extreme events, co-occurring or compound extremes may substantially increase risks.
To adequately address such risks, improving our understanding of compound flood events in Europe is necessary and requires reliable estimates of their probability of occurrence together with potential future changes.
In this study compound flood events in northern and central Europe were studied using a Monte Carlo-based approach that avoids the use of copulas.
Second, we investigate if the number of observed compound extreme events is within the expected range of 2Â standard deviations of randomly occurring compound events. This includes variations of several parameters to test the stability of the identified patterns. Finally, we analyse if the observed compound extreme events had a common large-scale meteorological driver.
The results of our investigation show that rivers along the west-facing coasts of Europe experienced a
higher amount of compound flood events than expected by pure chance.
In these regions, the vast majority of the observed compound flood events seem to be related to the cyclonic westerly general weather pattern (GroĂźwetterlage).</p
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Sensitive quantitative detection/identification of infectious Cryptosporidium parvum oocysts by signature lipid biomarker analysis
Unique signature lipid biomarkers were found in the acid-fast oocytes of Cryptosporidium parvum. This makes possible the rapid detection/identification and potential infectivity directly from drinking water membrane filtrates
Interactive impacts of meteorological and hydrological conditions on the physical and biogeochemical structure of a coastal system
The German Bight was exposed to record high riverine discharges in June 2013, as a result of flooding of the Elbe and Weser rivers. Several anomalous observations suggested that the hydrodynamical and biogeochemical states of the system were impacted by this event. In this study, we developed a biogeochemical model and coupled it with a previously introduced high-resolution hydrodynamical model of the southern North Sea in order to better characterize these impacts and gain insight into the underlying processes. Performance of the model was assessed using an extensive set of in situ measurements for the period 2011–2014. We first improved the realism of the hydrodynamic model with regard to the representation of cross-shore gradients, mainly through inclusion of flow-dependent horizontal mixing. Among other characteristic features of the system, the coupled model system can reproduce the low salinities, high nutrient concentrations and low oxygen concentrations in the bottom layers observed within the German Bight following the flood event. Through a scenario analysis, we examined the sensitivity of the patterns observed during July 2013 to the hydrological and meteorological forcing in isolation. Within the region of freshwater influence (ROFI) of the Elbe–Weser rivers, the flood event clearly dominated the changes in salinity and nutrient concentrations, as expected. However, our findings point to the relevance of the peculiarities in the meteorological conditions in 2013 as well: a combination of low wind speeds, warm air temperatures and cold bottom-water temperatures resulted in a strong thermal stratification in the outer regions and limited vertical nutrient transport to the surface layers. Within the central region, the thermal and haline dynamics interactively resulted in an intense density stratification. This intense stratification, in turn, led to enhanced primary production within the central region enriched by nutrients due to the flood but led to reduction within the nutrient-limited outer region, and it caused a widespread oxygen depletion in bottom waters. Our results further point to the enhancement of the current velocities at the surface as a result of haline stratification and to intensification of the thermohaline estuarine-like circulation in the Wadden Sea, both driven by the flood event
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