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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,387 records · Page 77
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Spatial variations in a.c. susceptibility and microstructure for the YBa2Cu3O(7-x) superconductor and their correlation with room-temperature ultrasonic measurements

The spatial (within-sample) uniformity of superconducting behavior and microstructure in YBa2Cu30(7-x) specimens over the pore fraction range of 0.10 to 0.25 was examined. The viability of using a room-temperature, nondestructive characterization method (ultrasonic velocity imaging) to predict spatial variability was determined. Spatial variations in superconductor properties were observed for specimens containing 0.10 pore fraction. An ultrasonic velocity image constructed from measurements at 1 mm increments across one such specimen revealed microstructural variation between edge and center locations that correlated with variations in alternating-current shielding and loss behavior. Optical quantitative image analysis on sample cross-sections revealed pore fraction to be the varying microstructural feature.

Roth, Don J.↗
NASA NTRS1991

Effect of Fiber Strength on the Room Temperature Tensile Properties of Sic/Ti-24Al-11Nb

SCA-6 SiC fibers of known strength were incorporated into SiC/Ti-24Al-11Nb (at. percent) composites and the effect of fiber strength variability on room temperature composite strength was investigated. Fiber was etched out of a composite fabricated by the powder cloth technique and the effect of the fabrication process on fiber strength was assessed. The strength of the composite was directly correlated with the strength of the as-received fiber. The strength of composite plates containing mixed fiber strengths was dominated by the lower strength fiber. Fabrication by the powder cloth technique resulted in only a slight degradation of fiber strength. The strength of the composite was found to be overestimated by the rule of mixtures strength calculation. Examination of failed tensile specimens revealed periodic fiber cracks and the failure mode was concluded to be cumulative. With the variation in fiber strength eliminated, the composite UTS was found to have a positive correlation with volume fraction of fiber.

Draper, S. L.↗
NASA NTRS1992

Long-term storage of salivary cortisol samples at room temperature

Collection of saliva samples for the measurement of cortisol during space flights provides a simple technique for studying changes in adrenal function due microgravity. In the present work, several methods for preserving saliva cortisol at room temperature were investigated using radioimmunoassays for determining cortisol in saliva samples collected on a saliva-collection device called Salivettes. It was found that a pretreatment of Salivettes with citric acid resulted in preserving more than 85 percent of the salivary cortisol for as long as six weeks. The results correlated well with those for a sample stored in a freezer on an untreated Salivette.

Chen, Yu-Ming↗
NASA NTRS1992

Failure mechanisms of 3-D woven SiC/SiC composites under tensile and flexural loading at room and elevated temperatures

Nicalon silicon carbide 3D yarn with silicon carbide matrix composites made through a chemical vapor infiltration (CVI) process were investigated under tensile and flexural loading at 23, 1200 and 1550 C in air. The effectiveness of a chemical vapor deposition (CVD) SiC surface coating was also evaluated in severe oxidizing environment. Acoustic emission sensors and in situ optical microscopy were used at room temperature to monitor the failure mechanisms. It is shown that the level of tensile stress at which nonlinear behavior begins is not drastically reduced at 1200 and 1550 C when composites were protected by a SiC surface coating. Extensive fiber pull-out was observed only in the 1550 C specimen. Similar behaviors were also found in flexural specimens.

Chulya, Abhisak↗
NASA NTRS1992

Fatigue and flexural response of advanced carbon-carbon composites at room and elevated temperatures

The flexural response of SiC-coated carbon-carbon composites (ACC-4) at room and elevated temperatures is presented. Three-point bending tests were performed on virgin and mission-cycled specimens, and the variation in flexural strength is examined. The load-deflection behavior of the material at various temperatures is investigated, and the Weibull (1939) analysis of the strength data is performed. Micrographs of various cross sections in the damaged zone were taken, and the failure mechanisms are discussed. Fatigue tests were conducted under flexural loads, and the S-N diagram with the corresponding Weibull analysis are presented. Untested as well as fractured specimens under static and dynamic loading were C-scanned to identify the damaged zone and visualize the extent of the damage. Failure analyses are presented for both static and cyclic loading on the basis of NDE, the micrographs, and the experimental data.

Mahfuz, Hassan↗
NASA NTRS1992

Room-temperature operation of MOCVD-grown GaInAs/InP strained-layer multiquantum well lasers in 1.8 micron range

The first successful room-temperature pulsed operation is reported of InGaAs strained layer multiquantum well injection lasers grown by MOVPE on InP substrates in the 1.8 micron range. The threshold current density and the external differential quantum efficiency of the 10 micron wide ridge waveguide lasers were 2.5 kA/sq cm (cavity length = 1 mm) and 5 percent (cavity length = 400 microns), respectively. Broad-area lasers, 100 microns wide and 1 mm long, had a reverse leakage current of less than 10 microamps at -1 V indicating high quality of the epitaxial layers.

Forouhar, S.↗
NASA NTRS1992

Virtual environment display for a 3D audio room simulation

The development of a virtual environment simulation system integrating a 3D acoustic audio model with an immersive 3D visual scene is discussed. The system complements the acoustic model and is specified to: allow the listener to freely move about the space, a room of manipulable size, shape, and audio character, while interactively relocating the sound sources; reinforce the listener's feeling of telepresence in the acoustical environment with visual and proprioceptive sensations; enhance the audio with the graphic and interactive components, rather than overwhelm or reduce it; and serve as a research testbed and technology transfer demonstration. The hardware/software design of two demonstration systems, one installed and one portable, are discussed through the development of four iterative configurations.

Chapin, William L.↗
NASA NTRS1953

Theoretical and Measured Attenuation of Mufflers at Room Temperature Without Flow, with Comments on Engine-exhaust Muffler Design

Equations are presented for the attenuation characteristics of several types of mufflers. Experimental curves of attenuation plotted against frequency are presented for 77 different mufflers and the results are compared with theory. The experiments were made at room temperature without flow and the sound source was a loud-speaker. A method is given for including the tail pipe in the calculations. The application of the theory to the design of engine-exhaust mufflers is discussed, and charts have been included for the assistance of the designer.

NOISE↗
NASA NTRS1993

New room temperature high resolution solid-state detector (CdZnTe) for hard x rays and gamma rays

The new CdZnTe high 'Z' material represents a significant improvement in detectors for high energy photons. With the thicknesses available, photons up to 100 keV can be efficiently detected. This material has a wide band gap of 1.5 - 2.2 eV which allows it to operate at room temperature while providing high spectral resolution. Results of resolution evaluations are presented. This detector can be used for high resolution spectral measurements of photons in x-ray and gamma-ray astronomy, offering a significant reduction in the weight, power, and volume of the detector system compared to more conventional detector types such as scintillation counters. In addition, the detector will have the simplicity and reliability of solid-state construction. The CdZnTe detector, as a new development, has not yet been evaluated in space. The Get Away Special program can provide this opportunity.

Stewart, Amyelizabeth C.↗
NASA NTRS1994

HFE safety reviews of advanced nuclear power plant control rooms

Advanced control rooms (ACR's) will utilize human-system interface (HSI) technologies that may have significant implications for plant safety in that they will affect the operator's overall role and means of interacting with the system. The Nuclear Regulatory Commission (NRC) reviews the human factors engineering (HFE) aspects of HSI's to ensure that they are designed to good HFE principles and support performance and reliability in order to protect public health and safety. However, the only available NRC guidance was developed more than ten years ago, and does not adequately address the human performance issues and technology changes associated with ACR's. Accordingly, a new approach to ACR safety reviews was developed based upon the concept of 'convergent validity'. This approach to ACR safety reviews is described.

Ohara, John↗
NASA NTRS1994

Mission Evaluation Room Intelligent Diagnostic and Analysis System (MIDAS)

The role of Mission Evaluation Room (MER) engineers is to provide engineering support during Space Shuttle missions, for Space Shuttle systems. These engineers are concerned with ensuring that the systems for which they are responsible function reliably, and as intended. The MER is a central facility from which engineers may work, in fulfilling this obligation. Engineers participate in real-time monitoring of shuttle telemetry data and provide a variety of analyses associated with the operation of the shuttle. The Johnson Space Center's Automation and Robotics Division is working to transfer advances in intelligent systems technology to NASA's operational environment. Specifically, the MER Intelligent Diagnostic and Analysis System (MIDAS) project provides MER engineers with software to assist them with monitoring, filtering and analyzing Shuttle telemetry data, during and after Shuttle missions. MIDAS off-loads to computers and software, the tasks of data gathering, filtering, and analysis, and provides the engineers with information which is in a more concise and usable form needed to support decision making and engineering evaluation. Engineers are then able to concentrate on more difficult problems as they arise. This paper describes some, but not all of the applications that have been developed for MER engineers, under the MIDAS Project. The sampling described herewith was selected to show the range of tasks that engineers must perform for mission support, and to show the various levels of automation that have been applied to assist their efforts.

Pack, Ginger L.↗
NASA NTRS1994

Human factors issues and approaches in the spatial layout of a space station control room, including the use of virtual reality as a design analysis tool

Human Factors Engineering support was provided for the 30% design review of the late Space Station Freedom Payload Control Area (PCA). The PCA was to be the payload operations control room, analogous to the Spacelab Payload Operations Control Center (POCC). This effort began with a systematic collection and refinement of the relevant requirements driving the spatial layout of the consoles and PCA. This information was used as input for specialized human factors analytical tools and techniques in the design and design analysis activities. Design concepts and configuration options were developed and reviewed using sketches, 2-D Computer-Aided Design (CAD) drawings, and immersive Virtual Reality (VR) mockups.

Hale, Joseph P., II↗
NASA NTRS1994

A Custom Robotic System for Inspecting HEPA Filters in the Payload Changeout Room at the NASA Kennedy Space Center

In this paper, the prime objective is to describe a custom 4-dof (degree-of-freedom) robotic arm capable of autonomously or telerobotically performing systematic HEPA filter inspection and certification in the Shuttle Launch Pad Payload Changeout Rooms (PCR's) on pads A and B at the Kennedy Space Center, Florida. This HEPA filter inspection robot (HFIR) has been designed to be easily deployable and is equipped with the necessary sensory devices, control hardware, software and man-machine interfaces needed to implement HEPA filter inspection reliably and efficiently without damaging the filters or colliding with existing PCR structures or filters. The main purpose of the HFIR is to implement an automated positioning system to move special inspection sensors in pre-defined or manual patterns for the purpose of verifying filter integrity and efficiency. This will ultimately relieve NASA Payload Operations from significant problems associated with time, cost and personnel safety, impacts realized during non-automated PCR HFIR filter certification.

Spencer, James E., Jr.↗
NASA NTRS1997

The Portable War Room Research Project

The Portable War Room is an internal TASC project to research and develop a visualization and simulation environment to provide for decision makers the power to review the past, understand the present, and peer into the future.

Govers, Francis X., III↗
NASA NTRS1960

An Exploratory Investigation of Some Factors Influencing the Room-Temperature Ductility of Tungsten

Specimens having an initial diameter of 0.125 inch were cut from commercially pure sintered and swaged tungsten rods. The effect of various surface treatments on the ductility of tungsten was evaluated by the use of a bend test. The criterion used to determine the relative ductilities was the final bend angle of the specimens. Results showed that the bend ductility of the tungsten specimens increased with increasing depths of the surface removed by electropolishing. When specimens electropolished to a depth sufficient to produce a marked increase in the ductility over that of the as-received surface condition were subsequently scratched with emery paper, the ductility achieved by electropolishing was greatly reduced. Removal of similar depths of the surface by grinding as were removed by electropolishing did not produce any appreciable increase in the ductility of the specimens. The ductility of specimens tested in the as-received surface condition and those having an electropolished surface exhibited a great sensitivity to deflection rate, the electropolished specimens being more ductile over the range of deflection rates tested. These exploratory results illustrated qualitatively the importance of surface condition on the room-temperature ductility of tungsten and indicated the importance of relatively fine scratches on the ductility of tungsten.

Stephens, Joseph R.↗
NASA NTRS1998

Room Temperature Tensile Behavior and Damage Accumulation of Hi-Nicalon Reinforced SiC Matrix Composites

Composites consisting of woven Hi-Nicalon fibers, BN interphases, and different SiC matrices were studied in tension at room temperature. Composites with SiC matrices processed by CVI and melt infiltration were compared. Monotonic and load/unload/reload tensile hysteresis experiments were performed. A modal acoustic emission (AE) analyzer was used to monitor damage accumulation during the tensile test. Post test polishing of the tensile gage sections was performed to determine the extent of cracking. The occurrence and location of cracking could easily be determined using modal AE. The loss of modulus could also effectively be determined from the change in the velocity of sound across the sample. Finally, the stresses where cracks appear to intersect the load-bearing fibers correspond with high temperature low cycle fatigue run out stresses for these materials.

Morscher, G. N.↗
NASA NTRS1999

New Technology CZT Detectors for High-Energy Flare Spectroscopy: The Room Temperature Semiconductor Spectrometer for JAWSAT

The goal of our Room Temperature Semiconductor Spectrometer (RTeSS) project is to develop a small high-energy solar flare spectrometer employing semiconductor detectors that do not require significant cooling when used as high-energy solar flare spectrometers. Specifically, the goal is to test Cadmium Zinc Telluride (CZT) detectors with coplanar grid electrodes as x-ray and gamma-ray spectrometers and to design an experiment that can be flown as a "piggy-back" payload on a satellite mission during the next solar maximum.

Vestrand, W. Thomas↗