5,681 research outputs found
Multi-Objective Gust Load Alleviation Control Designs for an Aeroelastic Wind Tunnel Demonstration Wing
This paper presents several control and gust disturbance estimation techniques applied to a mathematical model of a physical flexible wing wind tunnel model used in ongoing tests at the University of Washington Aeronautical Laboratory's Kirsten Wind Tunnel. Three methods of gust disturbance estimation are presented, followed by three control methods: LQG, Basic Multi-Objective (BMO), and a novel Multi-Objective Prediction Correction (MOPC) controller. The latter of which augments a multi-objective controller, and attempts to correct for errors in the disturbance estimate. A simplified linear simulation of the three controllers is performed and a simple MIMO stability and robustness assessment is performed. Then, the same controllers are simulated in a higher fidelity Simulink environment that captures sampling, saturation and noise effects. This preliminary analysis indicates that the BMO controller provides the best performance and largest stability margins
Elucidating the role of hyperfine interactions on organic magnetoresistance using deuterated aluminium tris(8-hydroxyquinoline)
Measurements of the effect of a magnetic field on the light output and
current through an organic light emitting diode made with deuterated aluminium
tris(8-hydroxyquinoline) have shown that hyperfine coupling with protons is not
the cause of the intrinsic organic magnetoresistance. We suggest that
interactions with unpaired electrons in the device may be responsible.Comment: Submitte
Defining Feedback: Understanding Students’ Perceptions of Feedback in the Introductory Communication Course
Feedback is an essential part of the teaching/learning processes. This statement is especially true in the introductory communication course where students receive feedback throughout the presentational speaking process. This paper explores how students define useful feedback based on 1,600 qualitative questionnaires that asked students about their perceptions of feedback. A thematic analysis of a randomly selected subset of 163 responses uncovered two themes: (1) feedback content characteristics (e.g., specific, constructive, praiseworthy, and purposive) and (2) process of instructor-provided feedback (e.g., iterative, timely). Based on these findings, a set of best practices for providing feedback is offered as a means to improve teaching/learning in the introductory communication course
Temperature dependent optical studies of TiCoO
We present the results of Raman and photoluminescence (PL) studies on
epitaxial anatase phase TiCoO films for = 0-0.07, grown by
pulsed laser deposition. The low doped system (=0.01 and 0.02) shows a Curie
temperature of ~700 K in the as-grown state. The Raman spectra from the doped
and undoped films confirm their anatase phase. The photoluminescence spectrum
is characterized by a broad emission from self-trapped excitons (STE) at 2.3 eV
at temperatures below 120 K. This peak is characteristic of the anatase-phase
TiO and shows a small blueshift with increasing doping concentration. In
addition to the emission from STE, the Co-doped samples show two emission lines
at 2.77 eV and 2.94 eV that are absent in the undoped film indicative of a
spin-flip energy.Comment: 8 pages, 4 figure
Measurement of the Far Infrared Magneto-Conductivity Tensor of Superconducting YBaCuO Thin Films
We report measurements of the far infrared transmission of superconducting
YBaCuO thin films from 5 cm to 200 cm in
fields up to 14. A Kramers-Kronig analysis of the magneto-transmission
spectrum yields the magneto-conductivity tensor. The result shows that the
magneto-conductivity of YBaCuO is dominated by three
terms: a London term, a low frequency Lorentzian ( 3 cm) of width 10 cm and a finite frequency Lorentzian of
width 17 cm at 24 cm in the hole
cyclotron resonance active mode of circular polarization.\\Comment: Revised LaTex file (12 pages) + 4 Postscript figures, uuencoded. In
response to referees' comments, we refined the paper a lot; we encourage you
to download this revised versio
Near-Infrared Spectroscopy of McNeil's Nebula Object
We present 0.8-5.2 micron spectroscopy of the compact source at the base of a
variable nebula (McNeil's Nebula Object) in the Lynds 1630 dark cloud that went
into outburst in late 2003. The spectrum of this object reveals an extremely
red continuum, CO bands at 2.3-2.5 microns in emission, a deep 3.0 micron ice
absorption feature, and a solid state CO absorption feature at 4.7 microns. In
addition, emission lines of H, Ca II, Mg I, and Na I are present. The Paschen
lines exhibit P Cygni profiles, as do two lines of He I, although the emission
features are very weak in the latter. The Brackett lines, however, are seen to
be purely in emission. The P Cygni profiles clearly indicate that mass outflow
is occurring in a wind with a velocity of ~400 km/s. The H line ratios do not
yield consistent estimates of the reddening, nor do they agree with the
extinction estimated from the ice feature (A_V ~ 11). We propose that these
lines are optically thick and are produced in a dense, ionized wind. The
near-infrared spectrum does not appear similar to any known FUor or EXor
object. However, all evidence suggests that McNeil's Nebula Object is a
heavily-embedded low-mass Class I protostar, surrounded by a disk, whose
brightening is due to a recent accretion event.Comment: 11 pages, 2 ps figures, accepted for publication in ApJ Letter
Magnetoresistance of YBa2Cu3O7 in the "cold spots" model
We calculate the in-plane magnetoresistance of
YBaCuO in a magnetic field applied perpendicular to the
planes for the ``cold spots'' model. In this model, the electron relaxation
time at small regions on the Fermi surface near the
Brillouin zone diagonals is much longer than the relaxation time
at the rest of the Fermi surface ( is temperature). In
qualitative agreement with the experiment, we find that Kohler's rule is
strongly violated, but the ratio ,
where is the Hall angle, is approximately
temperature-independent. We find the ratio is about 5.5, which is of the same
order of magnitude as in the experiment.Comment: RevTeX, 4 pages, 6 figures. V.2: 2 references adde
Composite vortex model of the electrodynamics of high- superconductor
We propose a phenomenological model of vortex dynamics in which the vortex is
taken as a composite object made of two components: the vortex current which is
massless and driven by the Lorentz force, and the vortex core which is massive
and driven by the Magnus force. By combining the characteristics of the
Gittleman-Rosenblum model (Phys. Rev. Lett. {\bf 16}, 734 (1966)) and Hsu's
theory of vortex dynamics (Physica {\bf C 213},305 (1993)), the model provides
a good description of recent far infrared measurements of the
magneto-conductivity tensor of superconducting YBaCuO
films from 5 cm to 200 cm.Comment: LaTex file (12 pages) + 3 Postscript figures, uuencoded. More
information on this paper, please check
http://www.wam.umd.edu/~lihn/newmodel
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