700 research outputs found
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
Modeling and Dynamic Analysis of Paralleled of dc/dc Converters with Master-Slave Current Sharing Control
A simple, application-oriented, transfer function model of paralleled converters employing Master-Slave Current-sharing (MSC) control is developed. Dynamically, the Master converter retains its original design characteristics; all the Slave converters are forced to depart significantly from their original design characteristics into current-controlled current sources. Five distinct loop gains to assess system stability and performance are identified and their physical significance is described. A design methodology for the current share compensator is presented. The effect of this current sharing scheme on 'system output impedance' is analyzed
The EU and Asia within an evolving global order: what is Europe? Where is Asia?
The papers in this special edition are a very small selection from those presented at the EU-NESCA (Network of European Studies Centres in Asia) conference on "the EU and East Asia within an Evolving Global Order: Ideas, Actors and Processes" in November 2008 in Brussels. The conference was the culmination of three years of research activity involving workshops and conferences bringing together scholars from both regions primarily to discuss relations between Europe and Asia, perceptions of Europe in Asia, and the relationship between the European regional project and emerging regional forms in Asia. But although this was the last of the three major conferences organised by the consortium, it in many ways represented a starting point rather than the end; an opportunity to reflect on the conclusions of the first phase of collaboration and point towards new and continuing research agendas for the future
The ELAIS Deep X-ray Survey
We present initial follow-up results of the ELAIS Deep X-ray Survey which is
being undertaken with the Chandra and XMM-Newton Observatories. 235 X-ray
sources are detected in our two 75 ks ACIS-I observations in the well-studied
ELAIS N1 and N2 areas. 90% of the X-ray sources are identified optically to
R=26 with a median magnitude of R=24. We show that objects which are unresolved
optically (i.e. quasars) follow a correlation between their optical and X-ray
fluxes, whereas galaxies do not. We also find that the quasars with fainter
optical counterparts have harder X-ray spectra, consistent with absorption at
both wavebands. Initial spectroscopic follow-up has revealed a large fraction
of high-luminosity Type 2 quasars. The prospects for studying the evolution of
the host galaxies of X-ray selected Type 2 AGN are considered.Comment: 9 pages, 5 figures, To appear in Proceedings of XXI Moriond
Conference: "Galaxy Clusters and the High Redshift Universe Observed in
X-rays", edited by D. Neumann, F.Durret, & J. Tran Thanh Va
The Limits of the Primitive Equations of Dynamics for Warm, Slowly Rotating Small Neptunes and Super Earths (article)
This is the author accepted manuscript. The final version is available from American Astronomical Society / IOP Publishing via the DOI in this record.The dataset associated with this article is located in ORE at: https://doi.org/10.24378/exe.1023We present significant differences in the simulated atmospheric flow for warm, tidally-locked small
Neptunes and super Earths (based on a nominal GJ 1214b) when solving the simplified, and commonly
used, primitive dynamical equations or the full Navier-Stokes equations. The dominant prograde,
superrotating zonal jet is markedly different between the simulations which are performed using practically identical numerical setups, within the same model. The differences arise due to the breakdown of the so-called `shallow-fluid' and traditional approximations, which worsens when rotation rates are slowed, and day{night temperature contrasts are increased. The changes in the zonal advection between simulations solving the full and simplified equations, give rise to significant differences in the atmospheric redistribution of heat, altering the position of the hottest part of the atmosphere and temperature contrast between the day and night sides. The implications for the atmospheric chemistry and, therefore, observations need to be studied with a model including a more detailed treatment of
the radiative transfer and chemistry. Small Neptunes and super Earths are extremely abundant and
important, potentially bridging the structural properties (mass, radius, composition) of terrestrial and
gas giant planets. Our results indicate care is required when interpreting the output of models solving
the primitive equations of motion for such planets.Leverhulme TrustScience and Technology Facilities CouncilEuropean Research Counci
Results from a set of three-dimensional numerical experiments of a hot Jupiter atmosphere.
ArticleThis is the author accepted manuscript. The final version is available from EDP Sciences via the DOI in this record.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
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