148 research outputs found
Identification of parameters in amplitude equations describing coupled wakes
We study the flow behind an array of equally spaced parallel cylinders. A
system of Stuart-Landau equations with complex parameters is used to model the
oscillating wakes. Our purpose is to identify the 6 scalar parameters which
most accurately reproduce the experimental data of Chauve and Le Gal [{Physica
D {\bf 58}}, pp 407--413, (1992)]. To do so, we perform a computational search
for the minimum of a distance \calj. We define \calj as the sum-square
difference of the data and amplitudes reconstructed using coupled equations.
The search algorithm is made more efficient through the use of a partially
analytical expression for the gradient . Indeed
can be obtained by the integration of a dynamical system propagating backwards
in time (a backpropagation equation for the Lagrange multipliers). Using the
parameters computed via the backpropagation method, the coupled Stuart-Landau
equations accurately predicted the experimental data from Chauve and Le Gal
over a correlation time of the system. Our method turns out to be quite robust
as evidenced by using noisy synthetic data obtained from integrations of the
coupled Stuart-Landau equations. However, a difficulty remains with
experimental data: in that case the several sets of identified parameters are
shown to yield equivalent predictions. This is due to a strong discretization
or ``round-off" error arising from the digitalization of the video images in
the experiment. This ambiguity in parameter identification has been reproduced
with synthetic data subjected to the same kind of discretization.Comment: 25 pages uuencoded compressed PostScript file (58K) with 13 figures
(155K in separated file) Submitted to Physica
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Visualization of Tonal Harmony for Jazz Lead Sheets
Jazz improvisation is the extemporaneous expression of melody, and musicians commonly base their performances on chord progressions given by lead sheets. It is standard practice to commit a progression to memory by analyzing it for common patterns. This paper presents a visualization design intended to help reduce the amount of cognitive work needed to assimilate a song’s chords and harmonic patterns. It does this using color, shapes, and glyphs as visual variables to convey meaning about tonal centers, chord functions, and harmonic structure
Estimating Nuisance Parameters in Inverse Problems
Many inverse problems include nuisance parameters which, while not of direct
interest, are required to recover primary parameters. Structure present in
these problems allows efficient optimization strategies - a well known example
is variable projection, where nonlinear least squares problems which are linear
in some parameters can be very efficiently optimized. In this paper, we extend
the idea of projecting out a subset over the variables to a broad class of
maximum likelihood (ML) and maximum a posteriori likelihood (MAP) problems with
nuisance parameters, such as variance or degrees of freedom. As a result, we
are able to incorporate nuisance parameter estimation into large-scale
constrained and unconstrained inverse problem formulations. We apply the
approach to a variety of problems, including estimation of unknown variance
parameters in the Gaussian model, degree of freedom (d.o.f.) parameter
estimation in the context of robust inverse problems, automatic calibration,
and optimal experimental design. Using numerical examples, we demonstrate
improvement in recovery of primary parameters for several large- scale inverse
problems. The proposed approach is compatible with a wide variety of algorithms
and formulations, and its implementation requires only minor modifications to
existing algorithms.Comment: 16 pages, 5 figure
Random field modeling for interpretation and analysis of layered data
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1987.MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERINGBibliography: leaves 288-290.by Carey David Bunks.Ph.D
Direct temperature and salinity acoustic full waveform inversion
5 pages, 4 figuresRecent work has shown that Full Waveform Inversion could be suitable to extract physical properties such as sound speed (c), density (ρ), temperature (T), and salinity (S) from the weak impedance contrasts associated with the ocean's thermohaline fine structure.The seismic inversion approaches proposed so far are based on the iterative inversion of c from multichannel seismic data, while the rest of parameters (T,S, and ρ) are determined in a second step using two equations of state and a local T-S empirical relationship. In this work, we present an alternative to this approach. Using 1-D synthetic seismic data, we demonstrate that the direct full waveform inversion of T and S using adjoint methods is feasible without the use of any local T-S relationship and that the models of physical properties obtained with this approach are far more accurate than those inferred from c. Key Points T and S can be inverted simultaneously from ocean acoustic data using FWI Local T-S empirical relationships are not required for the inversion Our T and S results have a potential density error of 0.01 kg/m3. © 2013. American Geophysical Union. All Rights ReservedThis work has been fulfilled in the framework of the project POSEIDON (CTM2010-25169) and APOGEO (CTM2011-16001-E/MAR), both funded by the Spanish Ministry of Economy and Competitiveness (MINECO), and the Marie Curie project OCEANSEIS (FP7-PEOPLE-2010-IOF-271936-OCEANSEIS)Peer Reviewe
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