6,764 research outputs found
Feedback control of unstable steady states of flow past a flat plate using reduced-order estimators
We present an estimator-based control design procedure for flow control,
using reduced-order models of the governing equations, linearized about a
possibly unstable steady state. The reduced models are obtained using an
approximate balanced truncation method that retains the most controllable and
observable modes of the system. The original method is valid only for stable
linear systems, and we present an extension to unstable linear systems. The
dynamics on the unstable subspace are represented by projecting the original
equations onto the global unstable eigenmodes, assumed to be small in number. A
snapshot-based algorithm is developed, using approximate balanced truncation,
for obtaining a reduced-order model of the dynamics on the stable subspace. The
proposed algorithm is used to study feedback control of 2-D flow over a flat
plate at a low Reynolds number and at large angles of attack, where the natural
flow is vortex shedding, though there also exists an unstable steady state. For
control design, we derive reduced-order models valid in the neighborhood of
this unstable steady state. The actuation is modeled as a localized body force
near the leading edge of the flat plate, and the sensors are two velocity
measurements in the near-wake of the plate. A reduced-order Kalman filter is
developed based on these models and is shown to accurately reconstruct the flow
field from the sensor measurements, and the resulting estimator-based control
is shown to stabilize the unstable steady state. For small perturbations of the
steady state, the model accurately predicts the response of the full
simulation. Furthermore, the resulting controller is even able to suppress the
stable periodic vortex shedding, where the nonlinear effects are strong, thus
implying a large domain of attraction of the stabilized steady state.Comment: 36 pages, 17 figure
Role of non-collective excitations in low-energy heavy-ion reactions
We investigate the effect of single-particle excitations on heavy-ion
reactions at energies near the Coulomb barrier. To this end, we describe
single-particle degrees of freedom with the random matrix theory and solve the
coupled-channels equations for one-dimensional systems. We find that the
single-particle excitations hinder the penetrability at energies above the
barrier, leading to a smeared barrier distribution. This indicates that the
single-particle excitations provide a promising way to explain the difference
in a quasi-elastic barrier distribution recently observed in Ne +
Zr systems.Comment: 8 pages, 7 figure
Collaborative Development and Evaluation of Text-processing Workflows in a UIMA-supported Web-based Workbench
Challenges in creating comprehensive text-processing worklows include a lack of the interoperability of individual components coming from different providers and/or a requirement imposed on the end users to know programming techniques to compose such workflows. In this paper we demonstrate Argo, a web-based system that addresses these issues in several ways. It supports the widely adopted Unstructured Information Management Architecture (UIMA), which handles the problem of interoperability; it provides a web browser-based interface for developing workflows by drawing diagrams composed of a selection of available processing components; and it provides novel user-interactive analytics such as the annotation editor which constitutes a bridge between automatic processing and manual correction. These features extend the target audience of Argo to users with a limited or no technical background. Here, we focus specifically on the construction of advanced workflows, involving multiple branching and merging points, to facilitate various comparative evalutions. Together with the use of user-collaboration capabilities supported in Argo, we demonstrate several use cases including visual inspections, comparisions of multiple processing segments or complete solutions against a reference standard, inter-annotator agreement, and shared task mass evaluations. Ultimetely, Argo emerges as a one-stop workbench for defining, processing, editing and evaluating text processing tasks
Subbarrier fusion reactions with dissipative couplings
Using the random matrix model, we discuss the effect of couplings to
non-collective states on the penetrability of a one dimensional potential
barrier. We show that these non-collective excitations hinder the penetrability
and thus smear the barrier distribution at energies above the barrier, while
they do not affect significantly the penetrability at deep subbarrier energies.
The energy dependence of the Q-value distribution obtained with this model is
also discussed.Comment: 4 pages, 2 figures. A talk given at the 10th international conference
on nucleus-nucleus collisions (NN2009), Aug. 16-21, 2009, Beijing, Chin
Non-collective excitations in low-energy heavy-ion reactions: applicability of the random-matrix model
We investigate the applicability of a random-matrix model to the description
of non-collective excitations in heavy-ion reactions around the Coulomb
barrier. To this end, we study fusion in the reaction O + Pb,
taking account of the known non-collective excitations in the Pb
nucleus. We show that the random-matrix model for the corresponding couplings
reproduces reasonably well the exact calculations, obtained using empirical
deformation parameters. This implies that the model may provide a powerful
method for systems in which the non-collective couplings are not so well known.Comment: 6 pages, 4 figure
Involution products in Coxeter groups
For W a Coxeter group, let
= {w ∈ W | w = xy where x, y ∈ W and x 2 = 1 = y 2}.
It is well known that if W is finite then W = . Suppose that w ∈ . Then the minimum value of ℓ(x) + ℓ(y) – ℓ(w), where x, y ∈ W with w = xy and x 2 = 1 = y 2, is called the excess of w (ℓ is the length function of W). The main result established here is that w is always W-conjugate to an element with excess equal to zero
Effects of nuclear structure on average angular momentum in subbarrier fusion
We investigate the effects of nuclear quadrupole and hexadecapole couplings
on the average angular momentum in sub-barrier fusion reactions. This quantity
could provide a probe for nuclear shapes, distinguishing between prolate vs.
oblate quadrupole and positive vs. negative hexadecapole couplings. We describe
the data in the O + Sm system and discuss heavier systems where shape effects
become more pronounced.Comment: Latex (uses the epsf macro), 10 pages of text, 3 postscript figures
included. Full postscript version available by anonymous ftp from
wisnuf.physics.wisc.edu:/pub/preprints. MAD-NT-94-0
A computer software system for integration and analysis of grid-based remote sensing data with other natural resource data. Remote Sensing Project
A computer-based information system is described designed to assist in the integration of commonly available spatial data for regional planning and resource analysis. The Resource Analysis Program (RAP) provides a variety of analytical and mapping phases for single factor or multi-factor analyses. The unique analytical and graphic capabilities of RAP are demonstrated with a study conducted in Windsor Township, Eaton County, Michigan. Soil, land cover/use, topographic and geological maps were used as a data base to develope an eleven map portfolio. The major themes of the portfolio are land cover/use, non-point water pollution, waste disposal, and ground water recharge
Robert Owen as a pioneer in industrial democracy and co-operativism
Thesis (M.A.)--Boston Universit
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