Wright-Patterson Air Force Base

About: Wright-Patterson Air Force Base is a other organization based out in Wright-Patterson AFB, Ohio, United States. It is known for research contribution in the topics: Laser & Mach number. The organization has 5817 authors who have published 9157 publications receiving 292559 citations. The organization is also known as: Wright-Patterson AFB & FFO.

Refractive-Index Measurements of Undoped Yttrium Aluminum Garnet from 0.4 to 5.0 mum.

Abstract: We report measurements of the refractive index of undoped yttrium aluminum garnet from 0.4 to 5.0 mum and the calculation of Sellmeier coefficients based on our data. The data differ considerably from previously published reports. The effect of the new data on the design of optical devices such as intracavity etalons for lasers is discussed.

Structure of laminar juncture flows

Abstract: A computational study of both steady and periodic laminar horseshoe vortex flows generated upstream of a cylinder/flat plate juncture is presented. The flowfields are simulated using the full three-dimensional unsteady Navier-Stokes equations and a time-accurate implicit algorithm. A new type of laminar horseshoe vortex topology is identified. For the case of a single primary vortex, this new topology is found to be independent of the computational grid and is also supported by recent experimental flow visualizations. The flat plate skin-friction portraits corresponding to the new and to the standard horseshoe vortex topologies are equivalent, pointing out the nonunique relation between the wall limiting streamline pattern and the three-dimensional flow above the plate. For the new topology, the foremost line of coalescense is an attachment rather than a separation line. This unusual feature illustrates the fact that convergence of skin-friction lines is a necessary but not sufficient condition for separation. As the Reynolds number increases, the flow topology evolves from a single to multiple primary horseshoe vortices, in agreement with experimental observations. At least two different types of triple horseshoe vortex systems are shown to be possible. Above a certain value of the Reynolds number, the juncture flow becomes unsteady and periodic at a frequency that increases with Reynolds number. The unsteady horseshoe vortex process upstream of the cylinder is found in qualitative agreement with experiment. Horseshoe vortices are periodically generated and convected toward the juncture. Vorticity intensification by vortex stretching, and the eruption of vorticity from the plate surface are observed.

Zero-Phonon Lines and Phonon Coupling in ZnS:Mn

Abstract: The optical absorption and emission spectra of several ZnS:Mn crystals (0.07 to 1.0 mole%) were obtained at 4.2 and 77\ifmmode^\circ\else\textdegree\fi{}K. Fine structure was observed in all bands. The predominant structure was identified in terms of phonon emission coupled to one electronic transition in each band. Zero-phonon lines were found at 17 891, 19 683, 21 237, 22 638, and 25 297 ${\mathrm{cm}}^{\ensuremath{-}1}$. They should correspond to transitions between some levels of the cubic crystalline field\char22{}terms such as $^{6}A_{1}\ensuremath{\rightarrow}^{4}T_{1}$, $^{6}A_{1}\ensuremath{\rightarrow}^{4}T_{2}$, $^{6}A_{1}\ensuremath{\rightarrow}^{4}E$, $^{6}A_{1}\ensuremath{\rightarrow}^{4}A_{1}$, etc. Principal phonons participating are of energies of about 86, (183,263), 298, and 340 ${\mathrm{cm}}^{\ensuremath{-}1}$. Possible mode assignments are pointed out. In conclusion, we suggest that the usually observed widths and shape of manganese bands are due predominantly to phonon coupling.

Dynamics and Control of a Biomimetic Vehicle Using Biased Wingbeat Forcing Functions

Abstract: A wingbeat forcing function and control method are presented that allow six-degree-of-freedom control of a flapping-wing micro air vehicle using only two actuators, each of which independently actuate a wing. Split-cycle constant-period frequency modulation with wing bias is used to produce nonzero cycle-averaged drag. The wing bias provides pitching-moment control and, when coupled with split-cycle constant-period frequency modulation, requires only independently actuated wings to enable six-degree-of-freedom flight. Wing bias shifts the cycle-averaged center-of-pressure locations of the wings, thus providing the ability to pitch the vehicle. Implementation of the wing bias is discussed, and modifications to the wingbeat forcing function are made to maintain wing position continuity. Instantaneous and cycle-averaged forces and moments are computed, cycle-averaged control derivatives are calculated, and a controller is developed. The controller is designed using a simplified aerodynamic model derived with blade-element theory and cycle averaging. The controller is tested using a simulation that includes blade-element-based estimates of the instantaneous aerodynamic forces and moments that are generated by the combined motion of the rigid-body fuselage and the flapping wings. Simulations using this higher-fidelity model indicate that the cycle-averaged blade-element-based controller is capable of achieving controlled flight.