26,170 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
Signature extension studies
The importance of specific spectral regions to signature extension is explored. In the recent past, the signature extension task was focused on the development of new techniques. Tested techniques are now used to investigate this spectral aspect of the large area survey. Sets of channels were sought which, for a given technique, were the least affected by several sources of variation over four data sets and yet provided good object class separation on each individual data set. Using sets of channels determined as part of this study, signature extension was accomplished between data sets collected over a six-day period and over a range of about 400 kilometers
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
The social geography of childcare: 'making up' the middle class child
Childcare is a condensate of disparate social forces and social processes. It is gendered and classed. It is subject to an excess of policy and political discourse. It is increasingly a focus for commercial exploitation. This is a paper reporting on work in progress in an ESRC funded research project (R000239232) on the choice and provision of pre-school childcare by middle class (service class) families in two contrasting London locations. Drawing on recent work in class analysis the paper examines the relationships between childcare choice, middle class fractions and locality. It suggests that on the evidence of the findings to date, there is some evidence of systematic differences between fractions in terms of values, perspectives and preferences for childcare, but a more powerful case for intra-class similarities, particularly when it comes to putting preferences into practice in the 'making up of a middle class child' through care and education
Verbal estimation of distance in a simulated space environment
Human performance in estimating distances in simulated space environmen
Multiple IMU system test plan, volume 4
Operating procedures for this redundant system are described. A test plan is developed with two objectives. First, performance of the hardware and software delivered is demonstrated. Second, applicability of multiple IMU systems to the space shuttle mission is shown through detailed experiments with FDI algorithms and other multiple IMU software: gyrocompassing, calibration, and navigation. Gimbal flip is examined in light of its possible detrimental effects on FDI and navigation. For Vol. 3, see N74-10296
Mie plasmons: modes volumes, quality factors and coupling strengths (Purcell factor) to a dipolar emitter
Using either quasi-static approximation or exact Mie expansion, we
characterize the localized surface plasmons supported by a metallic spherical
nanoparticle. We estimate the quality factor and define the effective
volume of the mode in a such a way that coupling strength with a
neighbouring dipolar emitter is proportional to the ratio (Purcell
factor). The role of Joule losses, far-field scattering and mode confinement in
the coupling mechanism are introduced and discussed with simple physical
understanding, with particular attention paid to energy conservation.Comment: (in press) International Journal of Optics (2011
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