Special Coverage

Distributed Propulsion Concepts and Superparamagnetic Energy Harvesting Hummingbird Engine
Aerofoam
Wet Active Chevron Nozzle for Controllable Jet Noise Reduction
Magnetic Relief Valve
Locking Mechanism for a Flexible Composite Hinge
Active Aircraft Pylon Noise Control System
Unmanned Aerial Systems Traffic Management
Method of Bonding Dissimilar Materials
Sonar Inspection Robot System
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Compact, Highly Stable Ion Atomic Clock

This high-precision clock is designed for navigation and radio science applications. A mercury-ion clock now at the breadboard stage of development (see figure) has a stability comparable to that of a hydrogen-maser clock: In tests, the clock exhibited an Allan deviation of between 2 × 10–13 and 3 × 10–13 at a measurement time of 1 second, averaging to about 10–15 at 1 day. However, the clock occupies a volume of only about 2 liters — about a hundredth of the volume of a hydrogen- maser clock. The ion- handling parts of the apparatus are housed in a sealed vacuum tube, wherein only a getter pump is used to maintain the vacuum. Hence, this apparatus is a prototype of a generation of small, potentially portable high-precision clocks for diverse ground- and space-based navigation and radio science applications. Furthermore, this new ion-clock technology is about 100 times more stable and precise than the rubidium atomic clocks currently in use in the NAVSTAR GPS Earth-orbiting satellites.

Posted in: Briefs, Physical Sciences

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Self-Deploying Trusses Containing Shape-Memory Polymers

Compacted structures can be used in shelters for hostile environments. Composite truss structures are being developed that can be compacted for stowage and later deploy themselves to full size and shape. In the target applications, these “smart” structures will precisely self-deploy and support a large, lightweight space-based antenna. Self-deploying trusses offer a simple, light, and affordable alternative to articulated mechanisms or inflatable structures. The trusses may also be useful in such terrestrial applications as variable-geometry aircraft components or shelters that can be compacted, transported, and deployed quickly in hostile environments.

Posted in: Briefs, Materials

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Refractory Ceramic Foams for Novel Applications

Properties could be tailored for specific uses as insulators, filters, or catalyst supports. Workers at NASA Ames Research center are endeavoring to develop durable, oxidation- resistant, foam thermal protection systems (TPSs) that would be suitable for covering large exterior spacecraft surfaces, would have low to moderate densities, and would have temperature capabilities comparable to those of carbon- based TPSs [reusable at 3,000 °F (≈1,650 °C)] with application of suitable coatings. These foams may also be useful for repairing TPSs while in orbit. Moreover, on Earth as well as in outer space, these foams might be useful as catalyst supports and filters.

Posted in: Briefs, TSP, Materials

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LiGa(OTf)4 as an Electrolyte Salt for Li-Ion Cells

This salt could improve rechargeable lithiumion cell performance. Lithium tetrakis(trifluoro- methanesulfonato) gallate [abbreviated “LiGa(OTf)4” (wherein “OTf” signifies trifluoro- methanesulfonate)] has been found to be promising as an electrolyte salt for incorporation into both liquid and polymer electrolytes in both rechargeable and non-rechargeable lithium-ion electro- chemical cells. This and other ingredients have been investigated in continuing research oriented toward improving the performances of rechargeable lithium-ion electrochemical cells, especially at low temperatures.

Posted in: Briefs, Physical Sciences

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Molecules for Fluorescence Detection of Specific Chemicals

These molecules could be used in the detection of chemical warfare agents. A family of fluorescent dye molecules has been developed for use in “on-off” fluorescence detection of specific chemicals. By themselves, these molecules do not fluoresce. However, when exposed to certain chemical analytes in liquid or vapor forms, they do fluoresce (see figure). These compounds are amenable to fixation on or in a variety of substrates for use in fluorescence-based detection devices: they can be chemically modified to anchor them to porous or non-porous solid supports or can be incorporated into polymer films. Potential applications for these compounds include detection of chemical warfare agents, sensing of acidity or alkalinity, and fluorescent tagging of proteins in pharmaceutical research and development. These molecules could also be exploited for use as two-photon materials for photodynamic therapy in the treatment of certain cancers and other diseases.

Posted in: Briefs, TSP, Materials

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Fuel-Cell Electrolytes Based on Organosilica Hybrid Proton Conductors

A new membrane composite material that combines an organosilica proton conductor with perfluorinated Nafion material to achieve good proton conductivity and high-temperature performance for membranes used for fuel cells in stationary, transportation, and portable applications has been developed.

Posted in: Briefs, Materials

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Single-Mode WGM Resonators Fabricated by Diamond Turning

Resonators having desired spectral responses can be reproduced efficiently. A diamond turning process has made possible a significant advance in the art of whispering-gallery- mode (WGM) optical resonators. By use of this process, it is possible to fashion crystalline materials into WGM resonators that have ultrahigh resonance quality factors (high Q values), are compact (ranging in size from millimeters down to tens of microns), and support single electromagnetic modes.

Posted in: Briefs, TSP, Physical Sciences

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