Physical Sciences

Preparing High-Quality Micrographic Samples of Oil Paintings

Cross-sectional specimens are prepared with wet grinding followed by dry polishing. A technique similar to that of metallography has been devised for preparing cross-sectional micrographic specimens from small samples cut from oil paintings. Art experts at the Cleveland Museum of Art use the technique in their efforts to determine painters’ methods and to verify the authenticity of paintings. By implementing the technique with automated polishing equipment, they can prepare a cross-sectional specimen in 20 min, and a publication-quality photomicrograph (see figure) can be made from the specimen. In contrast, the prior manual preparation technique took about 4 h and yielded specimens that contained scratches and were not flat enough for viewing at higher magnifications.

Posted in: Briefs, TSP, Physical Sciences, Imaging and visualization, Research and development, Materials identification


Pyrolytic-Graphite Gauges for Measuring Large Heat Fluxes

These gauges exploit the high-temperature endurance and thermal-conduction anisotropy of pyrolytic graphite. Gauges made of slugs of pyrolytic graphite with thermocouples em- bedded in them have been invented for use in measuring large, short-duration heat fluxes in hot, highly corrosive environments. These gauges were originally intended for use in combustion chambers of rocket engines; they might also be useful in terrestrial combustion chambers (e.g., in furnaces) and metal-processing equipment.

Posted in: Briefs, Physical Sciences, Measurements, Thermodynamics, Conductivity, Graphite, Test equipment and instrumentation


Wind and Mountain Wave Observations From a Flight Test of a Solar-Powered Airplane

This airplane was shown to be useful for observing atmospheric waves.In support of NASA’s Environmental Research Aircraft and Sensor Technology (ERAST) program, flight tests of the Pathfinder solar-electric-powered, remotely piloted aircraft (RPA) were conducted at the Navy’s Pacific Missile Range Facility (PMRF), Barking Sands, Kaua’i, Hawaii, from May to November 1997 and from June to August 1998. This airplane was designed to operate at low speeds and low Reynolds numbers for long duration at altitudes above 60,000 ft (18 km). Three successive altitude world records for propellerdriven aircraft were established during these tests: 67,400 ft (20.54 km) on June 9, 1997; 71,350 ft (21.75 km) on July 7, 1997; and 80,201 ft (24.445 km) on August 6, 1998.

Posted in: Briefs, TSP, Physical Sciences, Radar, Solar energy, Flight tests, Unmanned aerial vehicles


Electrostatic Systems Keep Dust Off Surfaces

These lightweight systems operate unattended and contain no moving parts. Electrostatic dust- collection systems that comprise wire grids connected to lightweight, low-power high-voltage sources have been invented for preventing the accumulation of dust on surfaces. Intended originally for use in keeping spacecraft solar panels free of dust, these systems could also be used on Earth to keep dust off such critical surfaces as those of semiconductor surfaces that await processing, highly sensitive optical instruments, and optoelectronic devices.

Posted in: Briefs, TSP, Physical Sciences, Optics, Semiconductors, Air cleaners, Spacecraft


System for Detecting Hazardous Gases at Multiple Locations

The Hazardous Gas Detection System 2000 (HGDS 2000) is the latest in a series of instrumentation systems for detecting gases leaking from a space shuttle on a launch pad. The HGDS is a fully redundant system that includes analog and digital electronic control circuitry and a sub- system for sampling gases at multiple locations and delivering the samples to two independent commercial quadrupole mass spectrometers. [The sampling subsystem was described in “System for Delivering Gas Samples to Multiple Instruments” (KSC-12123), NASA Tech Briefs, Vol. 25, No. 6 (June 2001), page 60.] The system is rugged enough to withstand the launch-pad environment, is easy to operate, and can be fully automated. When in automated operation, the system notifies an operator if an unusual situation or a fault is detected. An operator interacts with the system via a personal computer by use of mouse and keyboard commands. Operation of the HGDS 2000 is expected to take substantially smaller amounts of operators’ time and to cost substantially less, relative to operation of the older instrumentation systems in this series. Although the HGDS 2000 is optimized for detecting leaking spacecraft-propellant gases, it can also be used to detect many other gases.

Posted in: Briefs, Physical Sciences


Temperature-Compensation Method for High-Temperature Strain Gauges

Strain gauge and temperature-compensation element are exposed to the same temperature. A relatively simple and inexpensive method of fabricating a temp- erature-compensation element for high- temperature strain gauges has been devised. This element, connected in the adjacent arm of a Wheatstone bridge, provides temperature compensation for an active strain gauge attached to the substrate. A method for accurately measuring structural static strains in harsh environments is an important requirement for future flight research of hypersonic vehicles and ground test articles. Sturdy, flight-worthy strain sensors must be developed for attachment to superalloys, new composite materials, and thermal-protection systems. With little deviation from standard Rokide flame-spray installation procedures, preliminary tests indicate viable data can be produced to operating temperatures of at least 1,700 °F (927 °C).

Posted in: Briefs, Physical Sciences


Narrowband Tunable Optical Filter Using Fiber Bragg Gratings

Research at Langley Research Center has developed a special fiber- Bragg grating optical filter for use in aircraft or spaceborne differential absorption lidar (DIAL) systems for measuring water vapor in the atmosphere of the Earth. The filter is an optical fiber containing two Bragg gratings that afford high reflectance in 10-pm-wide wavelength bands at wavelengths of 946.0 and 949.5 nm. The optical fiber would be glued to a piezoelectric ceramic, to which a voltage could be applied to stretch the gratings and thereby adjust their peak-reflection wavelengths to correspond to atmospheric water vapor lines of interest. The concept of multiple Bragg gratings in a single optical fiber tuning such gratings by stretching the fiber is not new. The novelty of this research lies partly in the application of these concepts to make tunable ultra-narrowband filters for the specific water vapor wavelengths in question. Another element of novelty in the proposal lies in the design of the DIAL instrument in which the filters would be used: The design calls for a unique optical receiver that would couple a lidar signal from a telescope to a filter of the type proposed, then using an optical circulator the light would be detected.

Posted in: Briefs, TSP, Physical Sciences, Measurements, Fiber optics, Lidar, Water


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