15,113 research outputs found
Physical Transport and Chemical Behavior of Dispersed Oil
During response operations, scientific information is provided to decision makers, such as the Federal On-Scene Coordinator (FOSC), state and federal trustees, and the public. The decision to use chemical dispersants during a response is made among all these parties, and during the Deepwater Horizon (DWH) oil spill the dispersant discussion included both surface and subsurface application of chemical dispersants. This paper is intended to provide perspective on research needs considered pre- and post-DWH oil spill related to response modeling and data collection needs for decision support of dispersant application and its potential effects. Given time constraints for implementing models and sampling strategies for response, requirements for data and types of questions to be addressed may be significantly different than requirements for research or damage assessment activities. At the time of this writing, just over a year after the successful response operations to cap the well, many studies are still in progress, and data are still being collected and evaluated to assess dispersant effectiveness and possible impacts. More information and research results will become available over the next months to years. Thus these research needs, as summarized for this workshop, should be evaluated again at a later time
Total-pressure measurement in pulsating flows
Pneumatic-type probe was used as comparison instrument with total pressure tubes to determine true average pressure and, thus, to determine if nonlinear averaging effects were significant. Since pneumatic probe is more complicated to use than a total-pressure tube, it is used only as a comparison instrument to determine extent of averaging effects
Synthetic 26Al emission from galactic-scale superbubble simulations
© 2019 The Author(s).Emission from the radioactive trace element 26Al has been observed throughout the Milky Way with the COMPTEL and INTEGRAL satellites. In particular the Doppler shifts measured with INTEGRAL connect 26Al with superbubbles, which may guide 26Al flows off spiral arms in the direction of Galactic rotation. In order to test this paradigm, we have performed galaxy-scale simulations of superbubbles with 26Al injection in a Milky Way-type galaxy. We produce all-sky synthetic ray emission maps of the simulated galaxies. We find that the 1809keV emission from the radioactive decay of 26Al is highly variable with time and the observer's position. This allows us to estimate an additional systematic variability of 0.2dex for a star formation rate derived from 26Al for different times and measurement locations in Milky Way-type galaxies. High-latitude morphological features indicate nearby emission with correspondingly high integrated gamma-ray intensities. We demonstrate that the 26Al scale height from our simulated galaxies depends on the assumed halo gas density. We present the first synthetic 1809keV longitude-velocity diagrams from 3D hydrodynamic simulations. The line-of-sight velocities for 26Al can be significantly different from the line-of-sight velocities associated with the cold gas. Over time, 26Al velocities consistent with the INTEGRAL observations, within uncertainties, appear at any given longitude, broadly supporting previous suggestions that 26Al injected into expanding superbubbles by massive stars may be responsible for the high velocities found in the INTEGRAL observations. We discuss the effect of systematically varying the location of the superbubbles relative to the spiral arms.Peer reviewedFinal Accepted Versio
M82 - A radio continuum and polarisation study II. Polarisation and rotation measures
The composition and morphology of the interstellar medium in starburst
galaxies has been well investigated, but the magnetic field properties are
still uncertain. The nearby starburst galaxy M82 provides a unique opportunity
to investigate the mechanisms leading to the amplification and reduction of
turbulent and regular magnetic fields. Possible scenarios of the contribution
of the magnetic field to the star-formation rate are evaluated. Archival data
from the VLA and WSRT were combined and re-reduced to cover the wavelength
regime between 3cm and 22cm. All observations revealed polarised emission in
the inner part of the galaxy, while extended polarised emission up to a
distance of 2kpc from the disk was only detected at 18cm and 22cm. The
observations hint at a magnetised bar in the inner part of the galaxy. We
calculate the mass inflow rate due to magnetic stress of the bar to 7.1 solar
masses per year, which can be a significant contribution to the star-formation
rate of M82 of approximately 13 solar masses per year. The halo shows polarised
emission, which might be the remnant of a regular disk field. Indications for a
helical field in the inner part of the outflow cone are provided. The coherence
length of the magnetic field in the centre is similar to the size of giant
molecular clouds. Using polarisation spectra more evidence for a close coupling
of the ionised gas and the magnetic field as well as a two-phase magnetic field
topology were found. Electron densities in the halo are similar to the ones
found in the Milky Way. The magnetic field morphology is similar to the one in
other nearby starburst galaxies with possible large-scale magnetic loops in the
halo and a helical magnetic field inside the outflow cones. The special
combination of a magnetic bar and a circumnuclear ring are able to
significantly raise the star-formation rate in this galaxy by magnetic braking
M82 - A radio continuum and polarisation study I. Data reduction and cosmic ray propagation
The potential role of magnetic fields and cosmic ray propagation for feedback
processes in the early Universe can be probed by studies of local starburst
counterparts with an equivalent star-formation rate. Archival data from the
WSRT was reduced and a new calibration technique introduced to reach the high
dynamic ranges needed for the complex source morphology of M82. This data was
combined with archival VLA data, yielding total power maps at 3cm, 6cm, 22cm
and 92cm. The data shows a confinement of the emission at wavelengths of 3/6cm
to the core region and a largely extended halo reaching up to 4kpc away from
the galaxy midplane at wavelengths of 22/92cm up to a sensitivity limit of
90muJy and 1.8mJy respectively. The results are used to calculate the magnetic
field strength in the core region to 98muG and to 24muG in the halo regions.
From the observation of free-free losses the filling factor of the ionised
medium could be estimated to 2%. We find that the radio emission from the core
region is dominated by very dense HII-regions and supernova remnants, while the
surrounding medium is filled with hot X-ray and neutral gas. Cosmic rays
radiating at frequencies higher than 1.4 GHz are suffering from high
synchrotron and inverse Compton losses in the core region and are not able to
reach the halo. Even the cosmic rays radiating at longer wavelengths are only
able to build up the observed kpc sized halo, when several starbursting periods
are assumed where the photon field density varies by an order of magnitude.
These findings together with the strong correlation between Halpha, PAH+, and
our radio continuum data suggests a magnetic field which is frozen into the
ionised medium and driven out of the galaxy kinematically.Comment: 17 pages, 17 figures, to be published in A&
On cross-beam monitoring of atmospheric winds and turbulence with two orbiting telescopes
Crossed beam monitoring of atmospheric winds and turbulence with two orbiting astronomical telescopes mounted on single spacecraf
Better safe than sorry: Risky function exploitation through safe optimization
Exploration-exploitation of functions, that is learning and optimizing a
mapping between inputs and expected outputs, is ubiquitous to many real world
situations. These situations sometimes require us to avoid certain outcomes at
all cost, for example because they are poisonous, harmful, or otherwise
dangerous. We test participants' behavior in scenarios in which they have to
find the optimum of a function while at the same time avoid outputs below a
certain threshold. In two experiments, we find that Safe-Optimization, a
Gaussian Process-based exploration-exploitation algorithm, describes
participants' behavior well and that participants seem to care firstly whether
a point is safe and then try to pick the optimal point from all such safe
points. This means that their trade-off between exploration and exploitation
can be seen as an intelligent, approximate, and homeostasis-driven strategy.Comment: 6 pages, submitted to Cognitive Science Conferenc
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