21,481 research outputs found
A Gain Scheduling Optimization Method Using Genetic Algorithms
Gain scheduling. the traditional method of providing adaptive control to a nonlinear system, has long been an ad hoc design process. Until recently; little theoretical guidance directed this practitioners\u27 art. For this reason a systematic study of this design process and its potential for optimization has never been accomplished. Additionally, the nonlinearities and the large search space involved in gain scheduling also precluded such an optimization study. Traditionally, the gain scheduling process has been some variation of a linear interpolation between discrete design points. By using powerful non-traditional optimization tools such as genetic algorithms there are ways of improving this design process. This thesis utilizes the power of genetic algorithms to optimally design a gain schedule. First, a design methodology is validated on a simple pole placement problem, then demonstrated for an F-18 Super-maneuverable Fighter. From this experience, a general gain scheduling design process is developed and presented
Dirac Fields in Loop Quantum Gravity and Big Bang Nucleosynthesis
Big Bang nucleosynthesis requires a fine balance between equations of state
for photons and relativistic fermions. Several corrections to equation of state
parameters arise from classical and quantum physics, which are derived here
from a canonical perspective. In particular, loop quantum gravity allows one to
compute quantum gravity corrections for Maxwell and Dirac fields. Although the
classical actions are very different, quantum corrections to the equation of
state are remarkably similar. To lowest order, these corrections take the form
of an overall expansion-dependent multiplicative factor in the total density.
We use these results, along with the predictions of Big Bang nucleosynthesis,
to place bounds on these corrections.Comment: 15 pages, 2 figures; v2: new discussion of relevance of quantum
gravity corrections (Sec. II) and new estimates (Sec. V
Optimizing baryon acoustic oscillation surveys – I. Testing the concordance ΛCDM cosmology
We optimize the design of future spectroscopic redshift surveys for
constraining the dark energy via precision measurements of the baryon acoustic
oscillations (BAO), with particular emphasis on the design of the Wide-Field
Multi-Object Spectrograph (WFMOS). We develop a model that predicts the number
density of possible target galaxies as a function of exposure time and
redshift. We use this number counts model together with fitting formulae for
the accuracy of the BAO measurements to determine the effectiveness of
different surveys and instrument designs. We search through the available
survey parameter space to find the optimal survey with respect to the dark
energy equation-of-state parameters according to the Dark Energy Task Force
Figure-of-Merit, including predictions of future measurements from the Planck
satellite. We optimize the survey to test the LambdaCDM model, assuming that
galaxies are pre-selected using photometric redshifts to have a constant number
density with redshift, and using a non-linear cut-off for the matter power
spectrum that evolves with redshift. We find that line-emission galaxies are
strongly preferred as targets over continuum emission galaxies. The optimal
survey covers a redshift range 0.8 < z < 1.4, over the widest possible area
(6000 sq. degs from 1500 hours observing time). The most efficient number of
fibres for the spectrograph is 2,000, and the survey performance continues to
improve with the addition of extra fibres until a plateau is reached at 10,000
fibres. The optimal point in the survey parameter space is not highly peaked
and is not significantly affected by including constraints from upcoming
supernovae surveys and other BAO experiments.Comment: 15 pages, 9 figure
Anisotropy of effective masses in CuInSe2
Anisotropy of the valence band is experimentally demonstrated in CuInSe2, a key component of the absorber layer in one of the leading thin-film solar cell technology. By changing the orientation of applied magnetic fields with respect to the crystal lattice, we measure considerable differences in the diamagnetic shifts and effective g-factors for the A and B free excitons. The resulting free exciton reduced masses are combined with a perturbation model for non-degenerate independent excitons and theoretical dielectric constants to provide the anisotropic effective hole masses, revealing anisotropies of 5.5 (4.2) for the A (B) valence bands
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