992 research outputs found
A Census of the Avifauna of the FAP 301 Project Area Addenda 1 and 2
Report issued on: issued July 25, 1996INHS Technical Report prepared for Illinois Department of Transportatio
Using the UM dynamical cores to reproduce idealised 3D flows
We demonstrate that both the current (New Dynamics), and next generation
(ENDGame) dynamical cores of the UK Met Office global circulation model, the
UM, reproduce consistently, the long-term, large-scale flows found in several
published idealised tests. The cases presented are the Held-Suarez test, a
simplified model of Earth (including a stratosphere), and a hypothetical
tidally locked Earth. Furthermore, we show that using simplifications to the
dynamical equations, which are expected to be justified for the physical
domains and flow regimes we have studied, and which are supported by the
ENDGame dynamical core, also produces matching long-term, large-scale flows.
Finally, we present evidence for differences in the detail of the planetary
flows and circulations resulting from improvements in the ENDGame formulation
over New Dynamics.Comment: 34 Pages, 23 Figures. Accepted for publication in Geoscientific Model
Development (pre-proof version
Slow slip and the transition from fast to slow fronts in the rupture of frictional interfaces
The failure of the population of micro-junctions forming the frictional
interface between two solids is central to fields ranging from biomechanics to
seismology. This failure is mediated by the propagation along the interface of
various types of rupture fronts, covering a wide range of velocities. Among
them are so-called slow fronts, which are recently discovered fronts much
slower than the materials' sound speeds. Despite intense modelling activity,
the mechanisms underlying slow fronts remain elusive. Here, we introduce a
multi-scale model capable of reproducing both the transition from fast to slow
fronts in a single rupture event and the short-time slip dynamics observed in
recent experiments. We identify slow slip immediately following the arrest of a
fast front as a phenomenon sufficient for the front to propagate further at a
much slower pace. Whether slow fronts are actually observed is controlled both
by the interfacial stresses and by the width of the local distribution of
forces among micro-junctions. Our results show that slow fronts are
qualitatively different from faster fronts. Since the transition from fast to
slow fronts is potentially as generic as slow slip, we anticipate that it might
occur in the wide range of systems in which slow slip has been reported,
including seismic faults.Comment: 35 pages, 5 primary figures, 6 supporting figures. Post-print version
with improvements from review process include
A mixed local and nonlocal supercritical Dirichlet problems
In this work, we consider a mixed local and nonlocal Dirichlet problem with
supercritical nonlinearity. We first establish a multiplicity result for the
problem
\begin{equation}
Lu=|u|^{p-2}u+\mu|u|^{q-2}u~~\text{in}~~\Omega,~~~~~
u=0~~\text{in}~~\mathbb{R}^N\setminus\Omega,~~~ (0.1)
\end{equation}
where for and
is a bounded domain. Precisely, we show that problem (0.1) for has a
positive solution as well as a sequence of sign-changing solutions with a
negative energy for small values of . Here can be either a scalar
function, or a vector valued function so that (0.1) turns into a system with
supercritical nonlinearity. Moreover, whenever the domain is symmetric, we also
prove the existence of symmetric solutions enjoying the same symmetry
properties. We shall also prove an existence result for the supercritical
Hamiltonian system \begin{equation} Lu=|v|^{p-2}v,~~~~~~~ Lv=|u|^{d-2}u+\mu
|u|^{q-2}u \end{equation} with the Dirichlet boundary condition on
where . Our method is variational, and in both problems the lack of
compactness for the supercritical problem is recovered by working on a closed
convex subset of an appropriate function space
A uniform analysis of HD209458b Spitzer/IRAC lightcurves with Gaussian process models
We present an analysis of Spitzer/IRAC primary transit and secondary eclipse
lightcurves measured for HD209458b, using Gaussian process models to
marginalise over the intrapixel sensitivity variations in the 3.6 micron and
4.5 micron channels and the ramp effect in the 5.8 micron and 8.0 micron
channels. The main advantage of this approach is that we can account for a
broad range of degeneracies between the planet signal and systematics without
actually having to specify a deterministic functional form for the latter. Our
results do not confirm a previous claim of water absorption in transmission.
Instead, our results are more consistent with a featureless transmission
spectrum, possibly due to a cloud deck obscuring molecular absorption bands.
For the emission data, our values are not consistent with the thermal inversion
in the dayside atmosphere that was originally inferred from these data.
Instead, we agree with another re-analysis of these same data, which concluded
a non-inverted atmosphere provides a better fit. We find that a solar-abundance
clear-atmosphere model without a thermal inversion underpredicts the measured
emission in the 4.5 micron channel, which may suggest the atmosphere is
depleted in carbon monoxide. An acceptable fit to the emission data can be
achieved by assuming that the planet radiates as an isothermal blackbody with a
temperature of K.Comment: 18 pages, 5 figures, 6 tables. Accepted by MNRA
Results from a set of three-dimensional numerical experiments of a hot Jupiter atmosphere
We present highlights from a large set of simulations of a hot Jupiter
atmosphere, nominally based on HD 209458b, aimed at exploring both the
evolution of the deep atmosphere, and the acceleration of the zonal flow or
jet. We find the occurrence of a super-rotating equatorial jet is robust to
changes in various parameters, and over long timescales, even in the absence of
strong inner or bottom boundary drag. This jet is diminished in one simulation
only, where we strongly force the deep atmosphere equator-to-pole temperature
gradient over long timescales. Finally, although the eddy momentum fluxes in
our atmosphere show similarities with the proposed mechanism for accelerating
jets on tidally-locked planets, the picture appears more complex. We present
tentative evidence for a jet driven by a combination of eddy momentum transport
and mean flow.Comment: 26 pages, 22 Figures. Accepted for publication in Astronomy and
Astrophysic
Habitable Climate Scenarios for Proxima Centauri b With a Dynamic Ocean
The nearby exoplanet Proxima Centauri b will be a prime future target for
characterization, despite questions about its retention of water. Climate
models with static oceans suggest that an Earth-like Proxima b could harbor a
small dayside region of surface liquid water at fairly warm temperatures
despite its weak instellation. We present the first 3-dimensional climate
simulations of Proxima b with a dynamic ocean. We find that an ocean-covered
Proxima b could have a much broader area of surface liquid water but at much
colder temperatures than previously suggested, due to ocean heat transport and
depression of the freezing point by salinity. Elevated greenhouse gas
concentrations do not necessarily produce more open ocean area because of
possible dynamic regime transitions. For an evolutionary path leading to a
highly saline present ocean, Proxima b could conceivably be an inhabited,
mostly open ocean planet dominated by halophilic life. For an ocean planet in
3:2 spin-orbit resonance, a permanent tropical waterbelt exists for moderate
eccentricity. Simulations of Proxima Centauri b may also be a model for the
habitability of planets receiving similar instellation from slightly cooler or
warmer stars, e.g., in the TRAPPIST-1, LHS 1140, GJ 273, and GJ 3293 systems.Comment: Submitted to Astrobiology; 38 pages, 12 figures, 5 table
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