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.

The geometry and nature of pinning points of ½ 〈110] unit dislocations in binary TiAl alloys

Abstract: The b = ½ 〈110] unit dislocations in deformed TiAl alloys exhibit a unique morphology, consisting of numerous pinning points along the dislocation line aligned roughly along the screw dislocation direction, and bowed-out segments between the pinning points. The three-dimensional arrangement of these dislocations has been characterized in detail, based on post-mortem weak-beam transmission electron microscopy observations in deformed binary Ti-50 at.% Al and Ti-52 at.% Al alloys. The bowed segments glide on parallel {111} primary planes, and the pinning points are jogs with a range of heights, up to a maximum of about 40 nm. The substructure evolution is consistent with dislocation glide involving frequent double cross-slip and consequent jog formation. The dislocations experience a large glide resistance during the forward (non-conservative) motion of these jogs. Pinning of unit dislocations is an intrinsic process in these alloys and is not related to the presence of interstitial-containing prec...

Design of nonlinear control laws for high-angle-of-attack flight

Abstract: High-angle-of-attack flight control laws are developed for a supermaneuvera ble fighter aircraft The methods of dynamic inversion and structured singular value synthesis are combined into an approach which addresses both the nonlinearity and robustness problems of flight at extreme operating conditions The primary purpose of the dynamic inversion control elements is to linearize the vehicle response across the flight envelope Structured singular value synthesis is used to design a dynamic controller which provides robust tracking to pilot commands The resulting control system achieves desired flying qualities and guarantees a large margin of robustness to uncertainties for high-angle-of-attack flight conditions High-fidelity nonlinear simulation results show that the combined dynamic inversion /structured singular value synthesis control law achieves a high level of performance in a realistic environment

TDDFT Study of One- and Two-Photon Absorption Properties: Donor−π−Acceptor Chromophores

Abstract: We report a comprehensive time-dependent density functional theory (TDDFT) study of one-photon and two-photon absorption (OPA and TPA, respectively) spectra for donor−π−acceptor molecules. The calculated excitation energies were generally shown to be in good agreement with experiment, particularly when compared to results from measurements carried out in a nonpolar solvent, although the oscillator strengths were overestimated in some cases. Calculated TPA cross sections applying the two-state approximation were shown to be highly dependent on the form of the line-shape function used. Although a good agreement with experimental TPA spectra was generally observed, the wide range in the experimentally measured values and lack of systematic experimental data on solvent effects limited a detailed comparison as yet.

Effect of microstructure on notch fatigue properties of Ti-6Al-4V

Abstract: The effect of microstructure on the notch fatigue properties of Ti-6A1-4V was investigated. Specimens with five distinctly different microstructures were tested and subsequently examined in detail. It was found that the notch fatigue performance of the alloy varied significantly as the microstructure was altered by heat treatment. The best high cycle fatigue strength was found in specimens heat treated above the beta transus temperature, containing an almost totally transformed acicular alpha structure. The fatigue performance of specimens with this microstructure appeared to be controlled by the size of the nucleated crack. It is suggested that at low stress levels the nucleated crack is limited in size to the width of a single alpha needle, while at high stresses the nucleated crack may be as large as an entire colony of similarly aligned alpha needles.

Influence of the Shape of Nanostructured Metal Surfaces on Adsorption of Single Peptide Molecules in Aqueous Solution

Abstract: Self-assembly and function of biologically modified metal nanostructures depend on surface-selective adsorption; however, the influence of the shape of metal surfaces on peptide adsorption mechanisms has been poorly understood. The adsorption of single peptide molecules in aqueous solution (Tyr(12) , Ser(12) , A3, Flg-Na(3) ) is investigated on even {111} surfaces, stepped surfaces, and a 2 nm cuboctahedral nanoparticle of gold using molecular dynamics simulation with the CHARMM-METAL force field. Strong and selective adsorption is found on even surfaces and the inner edges of stepped surfaces (-20 to -60 kcal/mol peptide) in contrast to weaker and less selective adsorption on small nanoparticles (-15 to -25 kcal/mol peptide). Binding and selectivity appear to be controlled by the size of surface features and the extent of co-ordination of epitaxial sites by polarizable atoms (N, O, C) along the peptide chain. The adsorption energy of a single peptide equals a fraction of the sum of the adsorption energies of individual amino acids that is characteristic of surface shape, epitaxial pattern, and conformation constraints (often β-strand and random coil). The proposed adsorption mechanism is supported and critically evaluated by earlier sequence data from phage display, dissociation constants of small proteins as a function of nanoparticle size, and observed shapes of peptide-stabilized nanoparticles. Understanding the interaction of single peptides with shaped metal surfaces is a key step towards control over self-organization of multiple peptides on shaped metal surfaces and the assembly of superstructures from nanostructures.