29,064 research outputs found
Continuous Data Assimilation with Stochastically Noisy Data
We analyze the performance of a data-assimilation algorithm based on a linear
feedback control when used with observational data that contains measurement
errors. Our model problem consists of dynamics governed by the two-dimension
incompressible Navier-Stokes equations, observational measurements given by
finite volume elements or nodal points of the velocity field and measurement
errors which are represented by stochastic noise. Under these assumptions, the
data-assimilation algorithm consists of a system of stochastically forced
Navier-Stokes equations. The main result of this paper provides explicit
conditions on the observation density (resolution) which guarantee explicit
asymptotic bounds, as the time tends to infinity, on the error between the
approximate solution and the actual solutions which is corresponding to these
measurements, in terms of the variance of the noise in the measurements.
Specifically, such bounds are given for the the limit supremum, as the time
tends to infinity, of the expected value of the -norm and of the
Sobolev norm of the difference between the approximating solution and the
actual solution. Moreover, results on the average time error in mean are
stated
The merger boom: an overview
Consolidation and merger of corporations ; Corporations ; Public policy
Are hostile takeovers different?
Consolidation and merger of corporations ; Corporations ; Stockholders
Simulating Brownian suspensions with fluctuating hydrodynamics
Fluctuating hydrodynamics has been successfully combined with several
computational methods to rapidly compute the correlated random velocities of
Brownian particles. In the overdamped limit where both particle and fluid
inertia are ignored, one must also account for a Brownian drift term in order
to successfully update the particle positions. In this paper, we present an
efficient computational method for the dynamic simulation of Brownian
suspensions with fluctuating hydrodynamics that handles both computations and
provides a similar approximation as Stokesian Dynamics for dilute and
semidilute suspensions. This advancement relies on combining the fluctuating
force-coupling method (FCM) with a new midpoint time-integration scheme we
refer to as the drifter-corrector (DC). The DC resolves the drift term for
fluctuating hydrodynamics-based methods at a minimal computational cost when
constraints are imposed on the fluid flow to obtain the stresslet corrections
to the particle hydrodynamic interactions. With the DC, this constraint need
only be imposed once per time step, reducing the simulation cost to nearly that
of a completely deterministic simulation. By performing a series of
simulations, we show that the DC with fluctuating FCM is an effective and
versatile approach as it reproduces both the equilibrium distribution and the
evolution of particulate suspensions in periodic as well as bounded domains. In
addition, we demonstrate that fluctuating FCM coupled with the DC provides an
efficient and accurate method for large-scale dynamic simulation of colloidal
dispersions and the study of processes such as colloidal gelation
The Color Distributions of Globular Clusters in Virgo Elliptical Galaxies
This Letter presents the color distributions of the globular cluster (GC)
systems of 12 Virgo elliptical galaxies, measured using data from the Hubble
Space Telescope. Bright galaxies with large numbers of detected GC's show two
distinct cluster populations with mean V-I colors near 1.01 and 1.26. The GC
population of M86 is a clear exception; its color distribution shows a single
sharp peak near V-I=1.03. The absence of the red population in this galaxy, and
the consistency of the peak colors in the others, may be indications of the
origins of the two populations found in most bright elliptical galaxies.Comment: 5 pages, 1 figure, to be published in ApJ Letters Corrections to
introductio
X-ray observations of IC348 in light of an updated cluster census
IC348 is an excellent laboratory for studies of low-mass star formation being
nearby, compact and rich. A Chandra observation was carried out early in the
satellite's lifetime. The extensive new data in optical and infrared
wavelengths accumulated in subsequent years have changed the cluster census
calling for a re-analysis of the X-ray data.Comment: poster paper to appear in Proc. of the 15th Workshop on Cool Stars,
Stellar Systems and the Su
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