31,035 research outputs found
Single-Mode Projection Filters for Modal Parameter Identification for Flexible Structures
Single-mode projection filters are developed for eigensystem parameter identification from both analytical results and test data. Explicit formulations of these projection filters are derived using the orthogonal matrices of the controllability and observability matrices in the general sense. A global minimum optimization algorithm is applied to update the filter parameters by using the interval analysis method. The updated modal parameters represent the characteristics of the test data. For illustration of this new approach, a numerical simulation for the MAST beam structure is shown by using a one-dimensional global optimization algorithm to identify modal frequencies and damping. Another numerical simulation of a ten-mode structure is also presented by using a two-dimensional global optimization algorithm to illustrate the feasibility of the new method. The projection filters are practical for parallel processing implementation
Projection filters for modal parameter estimate for flexible structures
Single-mode projection filters are developed for eigensystem parameter estimates from both analytical results and test data. Explicit formulations of these projection filters are derived using the pseudoinverse matrices of the controllability and observability matrices in general use. A global minimum optimization algorithm is developed to update the filter parameters by using interval analysis method. Modal parameters can be attracted and updated in the global sense within a specific region by passing the experimental data through the projection filters. For illustration of this method, a numerical example is shown by using a one-dimensional global optimization algorithm to estimate model frequencies and dampings
k2U: A General Framework from k-Point Effective Schedulability Analysis to Utilization-Based Tests
To deal with a large variety of workloads in different application domains in
real-time embedded systems, a number of expressive task models have been
developed. For each individual task model, researchers tend to develop
different types of techniques for deriving schedulability tests with different
computation complexity and performance. In this paper, we present a general
schedulability analysis framework, namely the k2U framework, that can be
potentially applied to analyze a large set of real-time task models under any
fixed-priority scheduling algorithm, on both uniprocessor and multiprocessor
scheduling. The key to k2U is a k-point effective schedulability test, which
can be viewed as a "blackbox" interface. For any task model, if a corresponding
k-point effective schedulability test can be constructed, then a sufficient
utilization-based test can be automatically derived. We show the generality of
k2U by applying it to different task models, which results in new and improved
tests compared to the state-of-the-art.
Analogously, a similar concept by testing only k points with a different
formulation has been studied by us in another framework, called k2Q, which
provides quadratic bounds or utilization bounds based on a different
formulation of schedulability test. With the quadratic and hyperbolic forms,
k2Q and k2U frameworks can be used to provide many quantitive features to be
measured, like the total utilization bounds, speed-up factors, etc., not only
for uniprocessor scheduling but also for multiprocessor scheduling. These
frameworks can be viewed as a "blackbox" interface for schedulability tests and
response-time analysis
d_{xy}-Density wave in fermion-fermion cold atom mixtures
We study density wave instabilities in a doubly-degenerate Fermi-Fermi
mixture with symmetry on a square lattice. For sufficiently
large on-site inter-species repulsion, when the two species of fermions are
both at half-filling, two conventional (-wave) number density waves are
formed with a -phase difference between them to minimize the inter-species
repulsion. Upon moving one species away from half-filling, an unconventional
density wave with -wave symmetry emerges. When both species are away
from the vicinity of half-filling, superconducting instabilities dominate. We
present results of a functional renormalization-group calculation that maps out
the phase diagram at weak couplings. Also, we provide a simple explanation for
the emergence of the -density wave phase based on a four-patch model.
We find a robust and general mechanism for -density-wave formation that
is related to the shape and size of the Fermi surfaces. The density imbalance
between the two species of fermions in the vicinity of half-filling leads to
phase-space discrepancy for different inter-species Umklapp couplings. Using a
phase space argument for leading corrections in the one-loop renormalization
group approach to fermions, we show that the phase-space discrepancy in our
system causes opposite flows for the two leading intra-species Umklapp
couplings and that this triggers the -density-wave instability.Comment: revised long version; 8 pages, 7 figure
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