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.

Photomechanical Response of Glassy Azobenzene Polyimide Networks

Abstract: We report the synthesis of amorphous, heat-resistant (Tg ranging from 220 to 246 °C) polyimides cross-linked with a novel tris(azobenzeneamine) cross-linker and examine the photodirected bending of cantilevers composed of these materials to exposure to linearly polarized, 442 nm light. Increasing the cross-linker concentration from 5 to 20 mol % in the network not only serves to increase the Tg and modulus but also results in a considerable increase in photomechanical response observed as an increase in bending angle from 5° to 20°. Adjustment of the orientation of the electric field of the light polarization to the cantilever axis is shown to generate forward and backward (bidirectional) bending. Upon removal of the incident light, the cantilevers exhibit photoelastic behavior by restoring to the original vertical position.

Lorentz-Invariant Equations of Motion of Point Masses in the General Theory of Relativity

Abstract: After a general discussion of the problem of motion in the general theory of relativity a simple derivation of the law of motion is given for single poles of the gravitational field, which is based on a method originally developed by Mathisson. This law follows from the covariant conservation law for the matter energy-momentum tensor alone, without reference to any field equations, and takes the form of a geodesic of the (unknown) metric. Expanding this metric in terms of a power series in a parameter gamma and using the Minkowski proper time to parametrize the world lines of the particles, the (Lorentz-invariant) form of the approximate laws of motion follows. A method is developed to obtain the equations of motion (including the explicit form of the metric in terms of the particle variables) from Einsiein's field equations. A systematic linearization procedure leads to a series of second-order differential equations for the metric; the nth order approximation of the equations of motion, as well as the explicit form of the matter tensor in (n + l)st order, is obtained as an integrability condition on the (n + l)st order opproximation for the metric. No coordinate conditions are required to obtain themore » general form of the equations of motion; they are needed only to reduce the approximation equations to wave equations and thus to allow their explicit integration in terms of retarded or symmetric potentials. In developing the approximation method it is shown that consistency requires that any set of approximate equations is solved up to'' rather than in'' nth order; this implies that the form of the lower-order metric be maintained, but the motion corresponding to the nth order solutions rather than to lower order ones. In particular, the equations for the first- order metric imply zero-order equations of motion which restrict the particles to zero acceleration; the equations for the second-order metric imply first-order equation of motion involving the first-order metric, but without the previous restriction. In the retarded case the equations of motion contain retarded interactions and radiation terms of the form familiar from electrodynamics; no such terms appear in the symmetric case. The equations of the symmetric case are derivable from a Fokker-type variational principle. The relation of the results obtained to work on Lorentz-invariant equations by other autnors is discussed. In Appendix I a discussion of alternative derivations is prescnted; Appendix II contains remarks on Wheeler-Feynman type considerations for general relativistic equations of motion. (auth)« less

The System Zirconia-Scandia

Abstract: The system zirconia-scandia was investigated using X-ray diffraction analysis, differential thermal analysis, metallographic analysis, and melting point studies. Results reveal the monoclinic α1 phase (0 to 2 mol% Sc2O3), the tetragonal α2’phase (5 to 8% Sc2O3), the rhombohedral β phase (9 to 13% Sc2O3), the rhombohedral γ phase (15 to 23% Sc2O3), the rhombohedral δ phase (24 to 40% Sc2O3), and the cubic % phase (77.5 to 100% Sc2O3). The monoclinic α1 phase and the tetragonal α2’phase were found to transform to the tetragonal α2 phase over a wide temperature range depending on composition. The β, γ, and α phases transformed to a cubic phase at temperatures of %600%, 1100%, and 1300%C, respectively. A maximum melting point of %2870%C was found at %10% Sc2O3 and a eutectic at %2400%C at 55% Sc2O3.

Atomistic simulations of homogeneous dislocation nucleation in single crystal copper

Abstract: Atomistic simulations are used to investigate how the stress required for homogeneous nucleation of partial dislocations in single crystal copper under uniaxial tension changes as a function of crystallographic orientation. Molecular dynamics is employed based on an embedded-atom method potential for Cu at 10 and 300 K. Results indicate that non-Schmid parameters are required to describe dislocation nucleation for certain single crystal orientations. Specifically, we find that the stereographic triangle can be divided into two regions: a region where dislocation nucleation is dominated by the conventional Schmid factor (the resolved shear stress in the direction of slip) and a region where dislocation nucleation is dominated by the normal factor (the resolved stress normal to the slip plane). A continuum relationship that incorporates Schmid and non-Schmid terms to correlate the stress required for dislocation nucleation over all tensile axis orientations within the stereographic triangle is presented. The significance of this work is that simulation results are cast into an atomistically inspired continuum formulation for partial dislocation loop nucleation in face-centered cubic single crystals.