6,521 research outputs found
A data assimilation algorithm for the subcritical surface quasi-geostrophic equation
In this article, we prove that data assimilation by feedback nudging can be
achieved for the three-dimensional quasi-geostrophic equation in a simplified
scenario using only large spatial scale observables on the dynamical boundary.
On this boundary, a scalar unknown (buoyancy or surface temperature of the
fluid) satisfies the surface quasi-geostrophic equation. The feedback nudging
is done on this two-dimensional model, yet ultimately synchronizes the
streamfunction of the three-dimensional flow. The main analytical difficulties
are due to the presence of a nonlocal dissipative operator in the surface
quasi-geostrophic equation. This is overcome by exploiting a suitable partition
of unity, the modulus of continuity characterization of Sobolev space norms,
and the Littlewood-Paley decomposition to ultimately establish various
boundedness and approximation-of-identity properties for the observation
operators.Comment: 28 pages, referee comments incorporated, references added, abstract
and introduction modified, main theorems cover full subcritical range of
dissipation, certain boundedness properties of observation operators extende
Continuous data assimilation with blurred-in-time measurements of the surface quasi-geostrophic equation
An intrinsic property of almost any physical measuring device is that it
makes observations which are slightly blurred in time. We consider a
nudging-based approach for data assimilation that constructs an approximate
solution based on a feedback control mechanism that is designed to account for
observations that have been blurred by a moving time average. Analysis of this
nudging model in the context of the subcritical surface quasi-geostrophic
equation shows, provided the time-averaging window is sufficiently small and
the resolution of the observations sufficiently fine, that the approximating
solution converges exponentially fast to the observed solution over time. In
particular, we demonstrate that observational data with a small blur in time
possess no significant obstructions to data assimilation provided that the
nudging properly takes the time averaging into account. Two key ingredients in
our analysis are additional boundedness properties for the relevant interpolant
observation operators and a non-local Gronwall inequality.Comment: 44 page
A Geometric Model for Odd Differential K-theory
Odd -theory has the interesting property that it admits an infinite number
of inequivalent differential refinements. In this paper we provide a bundle
theoretic model for odd differential -theory using the caloron
correspondence and prove that this refinement is unique up to a unique natural
isomorphism. We characterise the odd Chern character and its transgression form
in terms of a connection and Higgs field and discuss some applications. Our
model can be seen as the odd counterpart to the Simons-Sullivan construction of
even differential -theory. We use this model to prove a conjecture of
Tradler-Wilson-Zeinalian regarding a related differential extension of odd
-theoryComment: 36 page
A new genus and species of pemphredonine wasp in Late Cretaceous Vendean amber (Hymenoptera: Crabronidae)
International audienceA new genus and species of pemphredonine wasp is described and figured in Late Cretaceous (Cenomanian to Santonian) amber from Vendée, in northwestern France. Menopsila dupeae n. gen. and sp., is based on a partial male preserved in a small sliver of translucent amber. The genus is placed incertae sedis within the Pemphredonini, as it intermingles features, likely plesiomorphies, of various lineages within the tribe. It likely represents a stem group to one or more of the constituent subtribes, yet it is arguably most similar to the Spilomenina.Un nouveau genre et une nouvelle espèce de guêpe pemphredonine sont décrits de l’ambre crétacé supérieur (Cénomanien à Santonien) de Vendée, nord-ouest de la France. Menopsila dupeae n. gen. et sp., est basé sur un mâle fragmentaire préservé dans un minuscule morceau d’ambre translucide. Le genre est placé incertae sedis au sein des Pemphredonini, car mêlant des caractères probablement plésiomorphes de plusieurs lignées de cette tribu. Il représente vraisemblablement un groupe souche de l’une ou plus des sous-tribus constitutives des Pemphredonini, mais il est sans doute plus proche des Spilomenina
The evolutionary development of high specific impulse electric thruster technology
Electric propulsion flight and technology demonstrations conducted primarily by Europe, Japan, China, the U.S., and the USSR are reviewed. Evolutionary mission applications for high specific impulse electric thruster systems are discussed, and the status of arcjet, ion, and magnetoplasmadynamic thrusters and associated power processor technologies are summarized
Relative Astrometry of Compact Flaring Structures in Sgr A* with Polarimetric VLBI
We demonstrate that polarimetric interferometry can be used to extract
precise spatial information about compact polarized flares of Sgr A*. We show
that, for a faint dynamical component, a single interferometric baseline
suffices to determine both its polarization and projected displacement from the
quiescent intensity centroid. A second baseline enables two-dimensional
reconstruction of the displacement, and additional baselines can self-calibrate
using the flare, enhancing synthesis imaging of the quiescent emission. We
apply this technique to simulated 1.3-mm wavelength observations of a "hot
spot" embedded in a radiatively inefficient accretion disk around Sgr A*. Our
results indicate that, even with current sensitivities, polarimetric
interferometry with the Event Horizon Telescope can achieve ~5 microarcsecond
relative astrometry of compact flaring structures near Sgr A* on timescales of
minutes.Comment: 9 Pages, 4 Figures, accepted for publication in Ap
Metabolomic profiling of macrophages determines the discrete metabolomic signature and metabolomic interactome triggered by polarising immune stimuli
Priming and activating immune stimuli have profound effects on macrophages, however, studies generally evaluate stimuli in isolation rather than in combination. In this study we have investigated the effects of pro-inflammatory and anti-inflammatory stimuli either alone or in combination on macrophage metabolism. These stimuli include host factors such as IFNÎł and ovalbumin-immunoglobulin immune complexes, or pathogen factors such as LPS. Untargeted LC-MS based metabolomics provided an in-depth profile of the macrophage metabolome, and revealed specific changes in metabolite abundance upon either individual stimuli or combined stimuli. Here, by factoring in an interaction term in the linear model, we define the metabolome interactome. This approach allowed us to determine whether stimuli interact in a synergistic or antagonistic manner. In conclusion this study demonstrates a robust approach to interrogate immune-metabolism, especially systems that model host-pathogen interactions
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