Physical Sciences

Thermal Technology System Acquires Heat Data to Count People

The Flowslide, developed by Royal Boon Edam Group Holding BV, is a combination of a revolving door and curved sliding panels, installed at Charles de Gaulle Airport, Paris. The Flowslide offers a complete physical separation between two crossing passenger flows on a single floor, allowing arriving and departing passengers to use a single door. The entry and exit points open and close alternatively within the curved wall of the revolving door, while keeping the passengers separate. As the two sets of passengers never come into contact with each other — despite using the same doorway — the Flowslide has enabled today's higher levels of security to be met, without the need to redevelop the terminal.

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Digital-Image Data Acquisition System for Turbulent Mixing and Combustion

An equipment and instrumentation system for high-speed digital image data acquisition and processing includes components for Planar Laser Induced Fluorescence (PLIF), flame-speed, and ignition and extinction measurements of laminar flames at variable pressure; tracking flow structures in a high-speed mixing layer using high-speed color schlieren; laser-beam manipulation and volume scanning for three-dimensional turbulence measurements; and an expanded infrastructure capability for processing experimental and numerical-simulation data.

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Perspective on Research in Laser Propulsion

A document summarizes the history of research on laser propulsion, starting with the first publication of the laser-propulsion concept in the year 1969, proceeding through studies of laser propulsion within the broader context of advanced propulsion systems in general, and culminating in proof-of-concept experiments and associated studies under the auspices of the Air Force Research Laboratory during the years 1996 through 2007. The document briefly discusses the basic physical principles and engineering concepts of laser propulsion as demonstrated in the proof-of-concept experiments, in which a model rocket denoted a laser lightcraft was lofted to altitudes exceeding 200 ft. (about 61 m). In these experiments, a CO2-laser beam of pulse energy of 400 J at a repetition rate of 25 Hz was used to vaporize a solid propellant (Delrin® polyoxymethylene) to generate thrust. There is a brief discussion of energy-conversion efficiency in laser propulsion. This is followed by an analysis of the concept of supplementing laser ablation energy, and thereby effectively increasing the energy-conversion efficiency, by incorporating a chemically energetic ingredient (ammonium nitrate) into the Delrin propellant. The document includes an extensive bibliography of research on laser propulsion.

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Some Advances in Understanding of Environmental Fatigue

A research program has yielded advances in understanding of numerous aspects of environmental crack propagation in aerospace aluminum alloys. From one perspective, the objective of this program was to quantitatively establish governing crack-tip-mechanics conditions and damage mechanisms pertinent to environmental crack propagation, using a combination of (1) high-spatial-resolution experimentation and (2) computational simulation based on continuum-mechanics mathematical models employing multiple length scales. From a slightly different perspective, the central goals of this research were to (1) develop means of accurate prediction of crack-tip stresses and plastic strains for incorporation into micromechanical descriptions of crack growth, (2) validate crack-tip-mechanics models by means of high-spatial-resolution experiments, and (3) resolve physical characteristics of damage attributable to accumulation of hydrogen at fatigue-crack tips.

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Cracking of Aluminum Panels Repaired With Composite Patches

An experimental study of the mechanical behavior of cracked aluminum specimens repaired with composite-material patches has yielded findings that may eventually contribute to the development of more- effective composite patches and of techniques for predicting and detecting failures in composite-patched aluminum aircraft panels. Some prior studies have addressed various aspects of composite-patch repair of aluminum specimens, but until now, little attention has been given to such important aspects of mechanical behavior and properties as the relationships among stress, strain, and growth of cracks through-out the lifetimes of specimens. In this study, effects of initiation and growth of cracks on the residual strengths of the patched specimens were characterized. This study established a correlation among damage modes, residual strengths, and evolution of strain inside and outside the patched areas.

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Improvements in Measurement of Permeability and Permittivity

The two-transmission method is an improved method of determining, from microwave measurements, the complex permeability and complex permittivity of a sample of a material typified by a lossy dielectric or a magnetic radar absorbing material. The two-transmission method is so named because it involves two microwave transmission- measurement runs: one on the sample alone and one on a two-layer stack comprising the sample plus a layer of an acrylic material that has known permittivity and permeability. The name of the two-transmission method also serves to distinguish it from a prior method that involves microwave-reflection measurements with which errors have been associated.

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Infrared-Sensitive Photorefractive Polymer Composite Devices

Polymer composites that are photorefractive at visible and near- infrared wavelengths, and devices that exploit their photorefractivity, have been demonstrated. Potential applications for such devices could include real-time holography, medical imaging, imaging through light-scattering media, and beam cleanup in free-space optical communications. Especially notable products of this development effort include devices that exhibit one-photon photorefractivity with high diffraction efficiency at a wavelength of about 1 μm and devices that exhibit two-photon photorefractivity at a wavelength of about 1.5 μm. The polymer composites used in these devices are the first-demonstrated all-organic photorefractive materials suitable for wavelengths >0.83 μm, and are among the best infrared-sensitive photorefractive materials yet demonstrated under similar experimental conditions.

Posted in: Briefs, Physical Sciences, Imaging, Composite materials, Polymers, Refractory materials
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Detecting Explosives by Use of LIBS

Laser-induced breakdown spectros - copy (LIBS) has been investigated for potential utility as a means of detecting trace amounts of chemical explosives and residues thereof in lawenforcement, forensic analysis, and military settings. In LIBS (see figure), a laser is used to rapidly generate a microplasma of a sample, and the light emitted by the microplasma is analyzed to identify (and determine the intensities of) spectral lines of elements and compounds in the sample. In previous applications for purposes other than detection of explosives, LIBS has been shown to enable remote, rapid, multielement micro-analysis of bulk samples (solid, liquid, gas, aerosol) of compounds having concentrations in the parts-per-million range.

Posted in: Briefs, Physical Sciences, Lasers, Spectroscopy, Chemicals, Hazards and emergency management, Rescue and emergency vehicles and equipment
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Mixing and Combustion in Turbulent, High-Speed Flows

A collection of reports presents a detailed description of a research program that focused on fundamental investigations of mixing and combustion in turbulent subsonic and supersonic flows like those encountered in high-speed air-breathing aircraft engines. The research included close coordination of effort between experiments and numerical simulations. Recent advances in instrumentation, including some made as part of this program, were utilized in the experiments. The research has been responsible for significant progress in the understanding of molecular mixing in high-speed flows in complicated geometries relevant to scramjet combustors and to high-speed aircraft engines in general. The research included a study oriented toward improving predictions of hydrocarbon flames in such flows and understanding the requirements for combustion of hydrocarbons and holding flames. The study involved comparisons of detailed experiments and detailed predictions of phenomena in stagnation-flame environments that replicate the fundamental effects that influence the stability and extinction of flames. An investigation of the three-dimensional structure of scalar dispersion, with a focus on grid turbulence, has been started and already has yielded new information with relevance to applications of turbulent mixing, including non-premixed combustion and dispersion of pollutants.

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Microcompression Tests of a BMG and a Tungsten/BMG Composite

Uniaxial-compression tests of micron-scale specimens (microcompression tests) of a bulk metallic glass (BMG) and of a tungsten/BMG composite have been performed to contribute to understanding of size-dependent mechanical properties of these and other, similar materials. There is increasing interest in fabricating micro- electromechanical systems from BMGs, and in fabricating kinetic-energy (ballistic) penetrators from BMGs and tungsten/ BMG composites. While the mechanical properties and deformation mechanisms of macroscopic, monolithic BMGs in bulk form are generally well understood, these properties are not necessarily equivalent for the BMG alloys cast in composite form or for micron-scale specimens. In a tungsten/BMG composite, dissolution of tungsten in the BMG matrix frequently manifests itself in the formation of complex crystalline phases and the concomitant decrease in the overall amorphous content of the matrix. Hence, it becomes important to compare the properties and deformation mechanisms of the monolithic BMG with those of the BMG as found in the composite accompanied by other phases and heterogeneities.

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