17,515 research outputs found
State-space model identification and feedback control of unsteady aerodynamic forces
Unsteady aerodynamic models are necessary to accurately simulate forces and
develop feedback controllers for wings in agile motion; however, these models
are often high dimensional or incompatible with modern control techniques.
Recently, reduced-order unsteady aerodynamic models have been developed for a
pitching and plunging airfoil by linearizing the discretized Navier-Stokes
equation with lift-force output. In this work, we extend these reduced-order
models to include multiple inputs (pitch, plunge, and surge) and explicit
parameterization by the pitch-axis location, inspired by Theodorsen's model.
Next, we investigate the na\"{\i}ve application of system identification
techniques to input--output data and the resulting pitfalls, such as unstable
or inaccurate models. Finally, robust feedback controllers are constructed
based on these low-dimensional state-space models for simulations of a rigid
flat plate at Reynolds number 100. Various controllers are implemented for
models linearized at base angles of attack , and . The resulting control laws are
able to track an aggressive reference lift trajectory while attenuating sensor
noise and compensating for strong nonlinearities.Comment: 20 pages, 13 figure
Response time to colored stimuli in the full visual field
Peripheral visual response time was measured in seven dark adapted subjects to the onset of small (45' arc diam), brief (50 msec), colored (blue, yellow, green, red) and white stimuli imaged at 72 locations within their binocular field of view. The blue, yellow, and green stimuli were matched for brightness at about 2.6 sub log 10 units above their absolute light threshold, and they appeared at an unexpected time and location. These data were obtained to provide response time and no-response data for use in various design disciplines involving instrument panel layout. The results indicated that the retina possesses relatively concentric regions within each of which mean response time can be expected to be of approximately the same duration. These regions are centered near the fovea and extend farther horizontally than vertically. Mean foveal response time was fastest for yellow and slowest for blue. Three and one-half percent of the total 56,410 trials presented resulted in no-responses. Regardless of stimulus color, the lowest percentage of no-responses occurred within 30 deg arc from the fovea and the highest within 40 deg to 80 deg arc below the fovea
A gallium phosphide high-temperature bipolar junction transistor
Preliminary results are reported on the development of a high temperature (350 C) gallium phosphide bipolar junction transistor (BJT) for geothermal and other energy applications. This four-layer p(+)n(-)pp(+) structure was formed by liquid phase epitaxy using a supercooling technique to insure uniform nucleation of the thin layers. Magnesium was used as the p-type dopant to avoid excessive out-diffusion into the lightly doped base. By appropriate choice of electrodes, the device may also be driven as an n-channel junction field-effect transistor. The initial design suffers from a series resistance problem which limits the transistor's usefulness at high temperatures
Isoprene oxidation by the gram-negative model bacterium variovorax sp. WS11
Plant-produced isoprene (2-methyl-1,3-butadiene) represents a significant portion of global volatile organic compound production, equaled only by methane. A metabolic pathway for the degradation of isoprene was first described for the Gram-positive bacterium Rhodococcus sp. AD45, and an alternative model organism has yet to be characterised. Here, we report the characterisation of a novel Gram-negative isoprene-degrading bacterium, Variovorax sp. WS11. Isoprene metabolism in this bacterium involves a plasmid-encoded iso metabolic gene cluster which differs from that found in Rhodococcus sp. AD45 in terms of organisation and regulation. Expression of iso metabolic genes is significantly upregulated by both isoprene and epoxyisoprene. The enzyme responsible for the initial oxidation of isoprene, isoprene monooxygenase, oxidises a wide range of alkene substrates in a manner which is strongly influenced by the presence of alkyl side-chains and differs from other well-characterised soluble diiron monooxygenases according to its response to alkyne inhibitors. This study presents Variovorax sp. WS11 as both a comparative and contrasting model organism for the study of isoprene metabolism in bacteria, aiding our understanding of the conservation of this biochemical pathway across diverse ecological niches
A quantum mechanical model of the upper bounds of the cascading contribution to the second hyperpolarizability
Microscopic cascading of second-order nonlinearities between two molecules
has been proposed to yield an enhanced third-order molecular nonlinear-optical
response. In this contribution, we investigate the two-molecule cascaded second
hyperpolarizability and show that it will never exceed the fundamental limit of
a single molecule with the same number of electrons as the two-molecule system.
We show the apparent divergence behavior of the cascading contribution to the
second hyperpolarizability vanishes when properly taking into account the
intermolecular interactions. Although cascading can never lead to a larger
nonlinear-optical response than a single molecule, it provides alternative
molecular design configurations for creating materials with large third-order
susceptibilities that may be difficult to design into a single molecule.Comment: 13 pages, 9 figures, 1 tabl
HI Absorption Toward HII Regions at Small Galactic Longitudes
We make a comprehensive study of HI absorption toward HII regions located
within Galactic longitudes less than 10 degrees. Structures in the extreme
inner Galaxy are traced using the longitude-velocity space distribution of this
absorption. We find significant HI absorption associated with the Near and Far
3kpc Arms, the Connecting Arm, Banias Clump 1 and the H I Tilted Disk. We also
constrain the line of sight distances to HII regions, by using HI absorption
spectra together with the HII region velocities measured by radio recombination
lines.Comment: Complete figure set available in online version of journal. Accepted
by ApJ August 8, 201
Exclusive Higgs Boson Production with bottom quarks at Hadron Colliders
We present the next-to-leading order QCD corrected rate for the production of
a scalar Higgs boson with a pair of high p_T bottom and anti-bottom quarks at
the Tevatron and at the Large Hadron Collider. Results are given for both the
Standard Model and the Minimal Supersymmetric Standard Model. The exclusive
b-bbar-h production rate is small in the Standard Model, but it can be greatly
enhanced in the Minimal Supersymmetric Standard Model for large tan(beta),
making b-bbar-h an important discovery mode. We find that the next-to-leading
order QCD results are much less sensitive to the renormalization and
factorization scales than the lowest order results, but have a significant
dependence on the choice of the renormalization scheme for the bottom quark
Yukawa coupling.Comment: 27 pages, 17 figures, RevTeX
Human immunodeficiency virus type 1 coat protein neurotoxicity mediated by nitric oxide in primary cortical cultures.
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