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 & Microstructure. The organization has 5817 authors who have published 9157 publications receiving 292559 citations. The organization is also known as: Wright-Patterson AFB & FFO.

MBO(N)D: A multibody method for long-time molecular dynamics simulations

Abstract: A modeling approach that can significantly speed up the dynamics simulation of large molecular systems is presented herein. A multigranular modeling approach, whereby different parts of the molecule are modeled at different levels of detail, is enabled by substructuring. Substructuring the molecular system is accomplished by collecting groups of atoms into rigid or flexible bodies. Body flexibility is modeled by a truncated set of body-based modes. This approach allows for the elimination of the high-frequency harmonic motion while capturing the low-frequency anharmonic motion of interest. This results in the use of larger integration step sizes, substantially reducing the computational time required for a given dynamic simulation. The method also includes the use of a multiple time scale (MTS) integration scheme. Speed increases of 5- to 30-fold over atomistic simulations have been realized in various applications of the method. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 159–184, 2000

Excitonic transitions in GaAs/GaxAl1-xAs quantum wells observed by photoreflectance spectroscopy: Comparison with a first-principles theory.

Abstract: Excitonic transitions in GaAs/${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$As multiple quantum wells are observed using photoreflectance spectra obtained with a novel double-monochrometer spectrometer. The first pass of the monochrometer produces the infrared probe beam while the second pass is used as a synchronous band-pass filter, resulting in a better signal-to-noise ratio than the low-pass filter conventionally used, and allowing simultaneous collection of the photoluminescence spectrum. The photoreflectance data are analyzed using a multiband effective-mass theory which includes valence-band mixing and assumes a first-derivative modulation of the built-in field as the dominant modulation mechanism. The entire photoreflectance spectrum is simultaneously fit using a first-principles theory in which only the exciton linewidth and value of the built-in electric field are not determined by the theory. Full advantage is thus taken of the signal intensity information, in contrast to comparisons currently encountered in the literature where positions of excitons are usually compared to values predicted by a finite-square-well calculation, without valence-band mixing effects. The theory is shown to have much success in explaining the observed photoreflectance signal from a 200-A\r{} multiple quantum well at 77 K, including the qualitative line shape for any given exciton.

Photochemical Mechanism and Photothermal Considerations in the Mechanical Response of Monodomain, Azobenzene-Functionalized Liquid Crystal Polymer Networks

Abstract: The potential for wireless transduction of input light energy into mechanical outputs has led to a reinvigorated pursuit of photomechanical effects in polymeric materials and composites. We report here on factors influencing the photochemical mechanism (and thus the mechanical output) in monodomain azobenzene-functionalized liquid crystal polymer networks. Through systematic examination of a representative material with both mechanics and spectroscopic characterization the prevalence of the trans–cis and trans–cis–trans mechanisms is elucidated. Furthermore, the role of light intensity in generating heat (photothermal effects) is also reported.

Continuous Coating of Oxide Fiber Tows Using Liquid Precursors: Monazite Coatings on Nextel 720™

Abstract: Seven different aqueous or ethanolic precursors were used to continuously coat monazite (LaPO4) on Nextel 720™ fiber tows. Immiscible liquid displacement was used to minimize bridging of coating between filaments. Precursor viscosities, densities, and concentrations were measured, and solids were characterized by DTA/TGA and X-ray. Coatings were cured in-line at 1200°-1400°C and characterized for thickness, microstructure, and composition by optical microscopy, SEM, and TEM. Tensile strengths of the coated fibers varied with the precursor used and were 25% to >50% lower than those of the as-received fiber. The coating stoichiometry and coating thickness of a particular precursor did not correlate with tensile strength. Median coating thicknesses were typically ∼50–100 nm for precursors with 40–80 g/L monazite, much larger than thicknesses predicted by theory for 12 mm diameter monofilaments. There were significant thickness variations from filament to filament, but usually little variation in composition or microstructure. Amorphous AlPO4 layers formed from phosphate-rich precursors. Factors that could affect coating characteristics and tensile strength reduction were discussed.