10,485 research outputs found
Vorticity-transport and unstructured RANS investigation of rotor-fuselage interactions
The prediction capabilities of unstructured primitive-variable and vorticity-transport-based Navier-Stokes solvers have been compared for rotorcraft-fuselage interaction. Their accuracies have been assessed using the NASA Langley ROBIN series of experiments. Correlation of steady pressure on the isolated fuselage delineates the differences between the viscous and inviscid solvers. The influence of the individual blade passage, model supports, and viscous effects on the unsteady pressure loading has been studied. Smoke visualization from the ROBIN experiment has been used to determine the ability of the codes to predict the wake geometry. The two computational methods are observed to provide similar results within the context of their physical assumptions and simplifications in the test configuration
Identifying Sources and Sinks in the Presence of Multiple Agents with Gaussian Process Vector Calculus
In systems of multiple agents, identifying the cause of observed agent
dynamics is challenging. Often, these agents operate in diverse, non-stationary
environments, where models rely on hand-crafted environment-specific features
to infer influential regions in the system's surroundings. To overcome the
limitations of these inflexible models, we present GP-LAPLACE, a technique for
locating sources and sinks from trajectories in time-varying fields. Using
Gaussian processes, we jointly infer a spatio-temporal vector field, as well as
canonical vector calculus operations on that field. Notably, we do this from
only agent trajectories without requiring knowledge of the environment, and
also obtain a metric for denoting the significance of inferred causal features
in the environment by exploiting our probabilistic method. To evaluate our
approach, we apply it to both synthetic and real-world GPS data, demonstrating
the applicability of our technique in the presence of multiple agents, as well
as its superiority over existing methods.Comment: KDD '18 Proceedings of the 24th ACM SIGKDD International Conference
on Knowledge Discovery & Data Mining, Pages 1254-1262, 9 pages, 5 figures,
conference submission, University of Oxford. arXiv admin note: text overlap
with arXiv:1709.0235
Constraints on the anisotropy of dark energy
If the equation of state of dark energy is anisotropic there will be
additional quadrupole anisotropy in the cosmic microwave background induced by
the time dependent anisotropic stress quantified in terms of .
Assuming that the entire amplitude of the observed quadrupole is due to this
anisotropy, we conservatively impose a limit of for any value of assuming that . This is
considerably tighter than that which comes from SNe. Stronger limits, upto a
factor of 10, are possible for specific values of and .
Since we assume this component is uncorrelated with the stochastic component
from inflation, we find that both the expectation value and the sample variance
are increased. There no improvement in the likelihood of an anomalously low
quadrupole as suggested by previous work on an elliptical universe
The atmospheric circulation of the super Earth GJ 1214b: Dependence on composition and metallicity
We present three-dimensional atmospheric circulation models of GJ 1214b, a
2.7 Earth-radius, 6.5 Earth-mass super Earth detected by the MEarth survey.
Here we explore the planet's circulation as a function of atmospheric
metallicity and atmospheric composition, modeling atmospheres with a low
mean-molecular weight (i.e., H2-dominated) and a high mean-molecular weight
(i.e. water- and CO2-dominated). We find that atmospheres with a low
mean-molecular weight have strong day-night temperature variations at pressures
above the infrared photosphere that lead to equatorial superrotation. For these
atmospheres, the enhancement of atmospheric opacities with increasing
metallicity lead to shallower atmospheric heating, larger day-night temperature
variations and hence stronger superrotation. In comparison, atmospheres with a
high mean-molecular weight have larger day-night and equator-to-pole
temperature variations than low mean-molecular weight atmospheres, but
differences in opacity structure and energy budget lead to differences in jet
structure. The circulation of a water-dominated atmosphere is dominated by
equatorial superrotation, while the circulation of a CO2-dominated atmosphere
is instead dominated by high-latitude jets. By comparing emergent flux spectra
and lightcurves for 50x solar and water-dominated compositions, we show that
observations in emission can break the degeneracy in determining the
atmospheric composition of GJ 1214b. The variation in opacity with wavelength
for the water-dominated atmosphere leads to large phase variations within water
bands and small phase variations outside of water bands. The 50x solar
atmosphere, however, yields small variations within water bands and large phase
variations at other characteristic wavelengths. These observations would be
much less sensitive to clouds, condensates, and hazes than transit
observations.Comment: 12 pages, 11 figures, 2 tables, accepted to Ap
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