Tech Briefs

Tool for Torquing Circular Electrical-Connector Collars

A simple tool exerts a strong grip. An improved tool has been devised for applying torque to lock and unlock knurled collars on circular electrical connectors. The tool was originally designed for, and used by, astronauts working in outer space on the Hubble Space Telescope (HST). The tool is readily adaptable to terrestrial use in installing and removing the same or similar circular electrical connectors as well as a wide variety of other cylindrical objects, the tightening and loosening of which entail considerable amounts of torque.

Posted in: Mechanics, Briefs, TSP

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Oxygen-Permeable, Hydrophobic Membranes of Silanized α-Al2O3

These membranes perform better than do organic polymer oxygen-diffusion membranes. Membranes made of silanized alumina have been prepared and tested as prototypes of derivatized ceramic membranes that are both highly permeable to oxygen and hydrophobic. Improved oxygen-permeable, hydrophobic membranes would be attractive for use in several technological disciplines, including supporting high-temperature aqueous-phase oxidation in industrial production of chemicals, oxygenation of aqueous streams for bioreactors, and oxygenation of blood during open-heart surgery and in cases of extreme pulmonary dysfunction. In comparison with organic polymeric oxygen-permeable membranes now commercially available, the derivatized ceramic membranes are more chemically robust, are capable of withstanding higher temperatures, and exhibit higher oxygen-diffusion coefficients.

Posted in: Briefs

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Thermoelectric Inhomogeneities in (Ag1-SbTe2)x(PbTe)1-x

A document presents a study of why materials of composition (Ag1–ySbTe2)0.05 (PbTe)0.95 [0=y=1] were previously reported to have values of the thermoelectric figure of merit [ZT (where Z = a2/??, a is the Seebeck coefficient, ? is electrical resistivity, ? is thermal conductivity, and T is absolute temperature)] ranging from 2. In the study, samples of (AgSbTe2)0.05(PbTe)0.95, (Ag0.67SbTe2)0.05 (PbTe)0.95, and (Ag0.55SbTe2)0.05(PbTe)0.95 were prepared by melting followed, variously, by slow or rapid cooling. Analyses of these samples by x-ray diffraction, electron microscopy, and scanning microprobe measurements of the Seebeck coefficient led to the conclusion that these materials have a multiphase character on a scale of the order of millimeters, even though they appear homogeneous in x-ray diffraction and electron microscopy. The Seebeck measurements showed significant variations, including both n-type and p-type behavior in the same sample. These variations were found to be consistent with observed variations of ZT. The rapidly quenched samples were found to be less inhomogeneous than were the furnace-cooled ones; hence, rapid quenching was suggested as a basis of research on synthesizing more nearly uniform high-ZT samples.

Posted in: Materials, Briefs, TSP

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SiC Composite Turbine Vanes

Y-cloth was conceived to provide fiber reinforcement for sharp trailing edges. Turbine inlet guide vanes have been fabricated from composites of silicon carbide fibers in silicon carbide matrices. A unique design for a cloth made from SiC fibers makes it possible to realize the geometric features necessary to form these vanes in the same airfoil shapes as those of prior metal vanes.

Posted in: Briefs, TSP

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Improved Oxygen-Beam Texturing of Glucose-Monitoring Optics

Textures can be more nearly optimized for greater utilization of light. An improved method has been devised for using directed, hyperthermal beams of oxygen atoms and ions to impart desired textures to the tips of polymethylmethacrylate [PMMA] optical fibers to be used in monitoring the glucose content of blood. The improved method incorporates, but goes beyond, the method described in “Texturing Blood- Glucose-Monitoring Optics Using Oxygen Beams” (LEW-17642- 1), NASA Tech Briefs, Vol. 29, No. 4 (April 2005), page 11a. The basic principle of operation of such a glucose-monitoring sensor is as follows: The textured surface of the optical fiber is coated with chemicals that interact with glucose in such a manner as to change the reflectance of the surface. Light is sent down the optical fiber and is reflected from, the textured surface. The resulting change in reflectance of the light is measured as an indication of the concentration of glucose.

Posted in: Briefs, TSP

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Prognostics Methodology for Complex Systems

Automatic method to detect and react to complex degradation and incipient faults. An automatic method to schedule maintenance and repair of complex systems is produced based on a computational structure called the Informed Maintenance Grid (IMG). This method provides solutions to the two fundamental problems in autonomic logistics: (1) unambiguous detection of deterioration or impending loss of function and (2) determination of the time remaining to perform maintenance or other corrective action based upon information from the system. The IMG provides a health determination over the medium-to-long-term operation of the system, from one or more days to years of study. The IMG is especially applicable to spacecraft and both piloted and autonomous aircraft, or industrial control processes.

Posted in: Briefs, TSP

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Modeling and Control of Aerothermoelastic Effects

This method makes it possible to design controls to compensate for aerothermoelasticity. Aerothermoelasticity comprises those aspects of the dynamics of an aircraft that are caused by flexibility and heating during flight. The concept of aerothermoelasticity is particularly important for hypersonic vehicles that operate at extremely high dynamic pressures. The design requirements for such vehicles often introduce long and thin fuselages subject to elastic bending in low- frequency vibrational modes. Furthermore, surface heating can significantly change the stiffness characteristics of these modes. These aerothermoelastic effects must be considered in the synthesis and analysis of control systems.

Posted in: Briefs

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