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.

Photoluminescence and lasing from deoxyribonucleic acid (DNA) thin films doped with sulforhodamine.

Abstract: Thin solid films of salmon deoxyribonucleic acid (DNA) have been fabricated by treatment with a surfactant and used as host for the laser dye sulforhodamine (SRh). The DNA films have an absorption peak at approximately 260 nm owing to absorption by the nitrogenous aromatic bases. The SRh molecules in the DNA films have absorption and emission peaks at 578 and 602 nm, respectively. The maximum emission was obtained at approximately 1 wt. % SRh in DNA, equivalent to approximately 100 DNA base pairs per SRh molecule. A distributed feedback grating structure was fabricated on a SiO(2)-Si substrate using interference lithography. The grating period of 437 nm was selected, corresponding to second-order emission at the amplified spontaneous emission wavelength of 650 nm. Lasing was obtained by pumping with a doubled Nd:YAG laser at 532 nm. The lasing threshold was 3 microJ, corresponding to approximately 30 microJ/cm(2) or 4 kW/cm(2). The emission linewidth decreased from approximately 30 nm in the amplified spontaneous emission mode to <0.4 nm (instrument limited) in the lasing mode. The slope efficiency of the lasing was approximately 1.2%.

The physical and mental health of a large military cohort: baseline functional health status of the Millennium Cohort

Abstract: Background: The US military is currently involved in large, lengthy, and complex combat operations around the world. Effective military operations require optimal health of deployed service members, and both mental and physical health can be affected by military operations.

Crystalline alumina deposited at low temperatures by ionized magnetron sputtering

Abstract: Ionized magnetron sputtering based on the work of Rossnagel and Hopwood [J. Vac. Sci. Technol. B 12, 449 (1994)] has been used to deposit alumina films containing orthorhombic κ alumina and monoclinic θ alumina at substrate temperatures of 370 to 430 °C. An inductively coupled rf Ar/O2/Al discharge between the sputter source and the heated substrate table was used to effectively ionize not only Ar but more importantly Al and O2. Both ion energy as well as the ion flux to the substrate influence the structure and properties of the coatings. The ion energy was controlled by the substrate bias potential, and the ion flux by means of the rf power supplied to the coil. The effect of the degree of ionization and therefore the ion flux to the substrate was studied at a constant substrate bias potential of −70 V. It was found that as the ion flux to the substrate was increased, the film crystallinity increased (i.e. the Bragg diffraction peaks were sharper and had higher intensity). It was shown that the formation temperature for κ alumina can be drastically decreased if high fluxes of reactive Al ions are employed to increase the energy at the substrate. Depending on the ion energy and ion flux, films with hardness values usually reported for chemical vapor deposition (CVD) κ alumina could be deposited at a maximum substrate temperature of 430 °C as opposed to ∼1000 °C by CVD. The process described allows for the first time the deposition of κ alumina onto metallic substrates such as hardened high speed steel without softening it.

Reliability Analysis of Aircraft Structures under Random Loading and Periodic Inspection

Abstract: A reliability analysis of fatigue-sensi tive aircraft structures, based on the application of the approach developed in the "random vibration theory," is presented. Operational service loads, composed of ground loads, ground-air-ground loads, and gust loads, are all random in nature. The fatigue process involved here consists of crack initiation, crack propagation, and strength degradation. The time to crack initiation and the ultimate strength are random variables. After a fatigue crack is initiated, fracture mechanics is applied to predict crack propagation under random loading. While the fatigue crack is propagating, the residual strength of the structure decreases progressively, thus increasing the failure rate with time. The aircraft structure is subjected to periodic inspection in service. When a fatigue crack is detected during inspection, the implicated component is either repaired or replaced, so that both the static and the fatigue strength are renewed. Such a renewal process is taken into account in the present analysis. The detection of an existing fatigue crack during inspection is also a random variable which depends on the resolution capability of the particular technique employed and the size of the existing crack. Taking into account all the random variables as well as all the random loadings, the solution for the probability of first failure in a fleet of aircraft is derived. Finally, numerical examples are given to demonstrate the effect of inspection and fleet size on the fleet reliability.

Effect of texture and slip mode on the anisotropy of plastic flow and flow softening during hot working of Ti-6Al-4V

Abstract: The effect of crystallographic texture and slip mode on the plastic flow of Ti-6Al-4V with either a colony- or globular-alpha microstructure was determined by conducting isothermal, constant-strainrate, hot-compression tests on specimens cut at various orientations (rolling direction (RD), transverse direction (TD), 45 deg, and normal) from hot-rolled plate. Testing was performed using a fixed strain rate (0.1 s−1) and various temperatures below the beta transus. The flow curves from all of the experiments exhibited a peak flow stress followed by a large and a small amount of flow softening for the colony and globular microstructures, respectively. Although the flow softening response did not depend noticeably on test direction for a given microstructure and test temperature, the peak flow stress and development of sample ovality did. This orientation dependence was interpreted using both lower-bound (isostress-type) and upper-bound (isostrain, Taylor/Bishop-Hill) models to deduce the operative slip systems in the alpha phase. These analyses suggested that prism 〈a〉 and basal 〈a〉 slip are considerably easier than pyramidal 〈c+a〉 or 〈a〉 slip at hot-working temperatures. A comparison of the flow curves for the colony and globular alpha microstructures suggested that slip transfer across alpha/beta interfaces and loss of Hall-Petch boundary strengthening can account for a substantial portion of the flow softening observed during hot working.