32,336 research outputs found
A Heuristic Framework for Next-Generation Models of Geostrophic Convective Turbulence
Many geophysical and astrophysical phenomena are driven by turbulent fluid
dynamics, containing behaviors separated by tens of orders of magnitude in
scale. While direct simulations have made large strides toward understanding
geophysical systems, such models still inhabit modest ranges of the governing
parameters that are difficult to extrapolate to planetary settings. The
canonical problem of rotating Rayleigh-B\'enard convection provides an
alternate approach - isolating the fundamental physics in a reduced setting.
Theoretical studies and asymptotically-reduced simulations in rotating
convection have unveiled a variety of flow behaviors likely relevant to natural
systems, but still inaccessible to direct simulation. In lieu of this, several
new large-scale rotating convection devices have been designed to characterize
such behaviors. It is essential to predict how this potential influx of new
data will mesh with existing results. Surprisingly, a coherent framework of
predictions for extreme rotating convection has not yet been elucidated. In
this study, we combine asymptotic predictions, laboratory and numerical
results, and experimental constraints to build a heuristic framework for
cross-comparison between a broad range of rotating convection studies. We
categorize the diverse field of existing predictions in the context of
asymptotic flow regimes. We then consider the physical constraints that
determine the points of intersection between flow behavior predictions and
experimental accessibility. Applying this framework to several upcoming devices
demonstrates that laboratory studies may soon be able to characterize
geophysically-relevant flow regimes. These new data may transform our
understanding of geophysical and astrophysical turbulence, and the conceptual
framework developed herein should provide the theoretical infrastructure needed
for meaningful discussion of these results.Comment: 36 pages, 8 figures. CHANGES: in revision at Geophysical and
Astrophysical Fluid Dynamic
An Exceptional Sector for F-theory GUTs
D3-branes are often a necessary ingredient in global compactifications of
F-theory. In minimal realizations of flavor hierarchies in F-theory GUT models,
suitable fluxes are turned on, which in turn attract D3-branes to the Yukawa
points. Of particular importance are ``E-type'' Yukawa points, as they are
required to realize a large top quark mass. In this paper we study the
worldvolume theory of a D3-brane probing such an E-point. D3-brane probes of
isolated exceptional singularities lead to strongly coupled N = 2 CFTs of the
type found by Minahan and Nemeschansky. We show that the local data of an
E-point probe theory determines an N = 1 deformation of the original N = 2
theory which couples this strongly interacting CFT to a free hypermultiplet.
Monodromy in the seven-brane configuration translates to a novel class of
deformations of the CFT. We study how the probe theory couples to the Standard
Model, determining the most relevant F-term couplings, the effect of the probe
on the running of the Standard Model gauge couplings, as well as possible
sources of kinetic mixing with the Standard Model.Comment: v2: 32 pages, 1 figure, references added, appendix remove
Magnetic Field Generation from Self-Consistent Collective Neutrino-Plasma Interactions
A new Lagrangian formalism for self-consistent collective neutrino-plasma
interactions is presented in which each neutrino species is described as a
classical ideal fluid. The neutrino-plasma fluid equations are derived from a
covariant relativistic variational principle in which finite-temperature
effects are retained. This new formalism is then used to investigate the
generation of magnetic fields and the production of magnetic helicity as a
result of collective neutrino-plasma interactions.Comment: 23 page
Magnetic inflation and stellar mass. IV. four low-mass kepler eclipsing binaries consistent with non-magnetic stellar evolutionary models
Low-mass eclipsing binaries (EBs) show systematically larger radii than model predictions for their mass, metallicity, and age. Prominent explanations for the inflation involve enhanced magnetic fields generated by rapid rotation of the star that inhibit convection and/or suppress flux from the star via starspots. However, derived
masses and radii for individual EB systems often disagree in the literature. In this paper, we continue to investigate low-mass EBs observed by NASA’s Kepler spacecraft, deriving stellar masses and radii using high-quality spacebased light curves and radial velocities from high-resolution infrared spectroscopy. We report masses and radii for three Kepler EBs, two of which agree with previously published masses and radii (KIC 11922782 and KIC 9821078). For the third EB (KIC 7605600), we report new masses and show the secondary component is likely fully convective (M2 = 0.17 ± 0.01M☉ and = - ☉ + R2 0.199 0.002R 0.001 ). Combined with KIC 10935310 from Han et al., we find that the masses and radii for four low-mass Kepler EBs are consistent with modern stellar evolutionary
models for M dwarf stars and do not require inhibited convection by magnetic fields to account for the stellar radii.Published versio
Effects of hemoglobin-based oxygen carriers on blood coagulation.
For many decades, Hemoglobin-based oxygen carriers (HBOCs) have been central in the development of resuscitation agents that might provide oxygen delivery in addition to simple volume expansion. Since 80% of the world population lives in areas where fresh blood products are not available, the application of these new solutions may prove to be highly beneficial (Kim and Greenburg 2006). Many improvements have been made to earlier generation HBOCs, but various concerns still remain, including coagulopathy, nitric oxide scavenging, platelet interference and decreased calcium concentration secondary to volume expansion (Jahr et al. 2013). This review will summarize the current challenges faced in developing HBOCs that may be used clinically, in order to guide future research efforts in the field
Analysis of Spitzer Spectra of Irradiated Planets: Evidence for Water Vapor?
Published mid infrared spectra of transiting planets HD 209458b and HD
189733b, obtained during secondary eclipse by the InfraRed Spectrograph (IRS)
aboard the Spitzer Space Telescope, are predominantly featureless. In
particular these flux ratio spectra do not exhibit an expected feature arising
from water vapor absorption short-ward of 10 um. Here we suggest that, in the
absence of flux variability, the spectral data for HD 189733b are inconsistent
with 8 um-photometry obtained with Spitzer's InfraRed Array Camera (IRAC),
perhaps an indication of problems with the challenging reduction of the IRS
spectra. The IRAC point, along with previously published secondary eclipse
photometry for HD 189733b, are in good agreement with a one-dimensional model
of HD 189733b that clearly shows absorption due to water vapor in the emergent
spectrum. We are not able to draw firm conclusions regarding the IRS data for
HD 209458b, but spectra predicted by 1D and 3D atmosphere models fit the data
adequately, without adjustment of the water abundance or reliance on cloud
opacity. We argue that the generally good agreement between model spectra and
IRS spectra of brown dwarfs with atmospheric temperatures similar to these
highly irradiated planets lends confidence in the modeling procedure.Comment: Revised, Accepted to ApJ Letter
A non-grey analytical model for irradiated atmospheres. II: Analytical vs. numerical solutions
The recent discovery and characterization of the diversity of the atmospheres
of exoplanets and brown dwarfs calls for the development of fast and accurate
analytical models. We quantify the accuracy of the analytical solution derived
in paper I for an irradiated, non-grey atmosphere by comparing it to a
state-of-the-art radiative transfer model. Then, using a grid of numerical
models, we calibrate the different coefficients of our analytical model for
irradiated solar-composition atmospheres of giant exoplanets and brown dwarfs.
We show that the so-called Eddington approximation used to solve the angular
dependency of the radiation field leads to relative errors of up to 5% on the
temperature profile. We show that for realistic non-grey planetary atmospheres,
the presence of a convective zone that extends to optical depths smaller than
unity can lead to changes in the radiative temperature profile on the order of
20% or more. When the convective zone is located at deeper levels (such as for
strongly irradiated hot Jupiters), its effect on the radiative atmosphere is
smaller. We show that the temperature inversion induced by a strong absorber in
the optical, such as TiO or VO is mainly due to non-grey thermal effects
reducing the ability of the upper atmosphere to cool down rather than an
enhanced absorption of the stellar light as previously thought.
Finally, we provide a functional form for the coefficients of our analytical
model for solar-composition giant exoplanets and brown dwarfs. This leads to
fully analytical pressure-temperature profiles for irradiated atmospheres with
a relative accuracy better than 10% for gravities between 2.5m/s^2 and 250
m/s^2 and effective temperatures between 100 K and 3000 K. This is a great
improvement over the commonly used Eddington boundary condition.Comment: Accepted in A&A, models are available at
http://www.oca.eu/parmentier/nongrey or in CD
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