SEARCH · Engineering Papers

Results for “characterization techniques”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 523 records · Page 29

All sources NASA NTRS DOE OSTI

NASA NTRS1981

Micro-area Auger analysis of a SiC/Ti fibre composite

Micro-area Auger electron spectroscopy with a spatial resolution of less than 50 nm has been used to study the concentration of elements across the reaction zone of a W-reinforced SiC fiber in a titanium matrix. Although the elemental concentrations obtained by this technique are affected by the reaction zone morphology to a greater extent than in the case of X-ray microprobe analysis, the proposed technique has the advantage of a much higher spatial resolution and avoids the problems of bulk averaging that characterize the X-ray technique.

Zironi, E. P.↗

NASA NTRS1995

Kinetics of cycle length dependence of ventricular repolarization: effect of autonomic blockade

INTRODUCTION: Beat-to-beat adaptation of ventricular repolarization duration to cardiac cycle length and autonomic activity has not been previously characterized in the spontaneously beating human heart. METHODS AND RESULTS: The ECG of 14 healthy subjects was recorded from the supine and upright positions. Autonomic blockade was accomplished by atropine and propranolol. RR and RT intervals were measured by a computer algorithm, and the impulse response (h) from RR to RT computed. In the supine position the maximal adjustment of the RT interval occurred in the first beat following a change in cycle length (hpeak = 17.8 +/- 1.6 msec/sec), but continued to be detectable for 3.8 seconds (2.9-4.7 sec). Propranolol attenuated the peak impulse response to 15.8 +/- 4.0 msec/sec (P = NS). In the standing position the peak impulse response was increased to 25.2 +/- 5.0 msec/sec (P = 0.004 vs supine), and the impulse response duration (hdur) shortened to 1.4 seconds (1.3-1.6). This was reversed by beta blockade (hpeak = 10.7 +/- 3.6 [P = 0.005 vs standing]; hdur = 5.5 sec [4.8-6.1]). Parasympathetic and combined autonomic blockade resulted in too little residual heart rate variability to estimate the impulse response accurately. The slope of the regression of delta RT and delta RR in the supine position was 0.0177 +/- 0.0016, which was closely correlated with the peak impulse response (r = 0.91). CONCLUSIONS: System identification techniques can assist in characterizing the cycle dependence of ventricular repolarization and may provide new insights into conditions associated with abnormal repolarization.

Clinical Trial↗

NASA NTRS1991

An empirical comparison of software fault tolerance and fault elimination

Reliability is an important concern in the development of software for modern systems. Some researchers have hypothesized that particular fault-handling approaches or techniques are so effective that other approaches or techniques are superfluous. The authors have performed a study that compares two major approaches to the improvement of software, software fault elimination and software fault tolerance, by examination of the fault detection obtained by five techniques: run-time assertions, multi-version voting, functional testing augmented by structural testing, code reading by stepwise abstraction, and static data-flow analysis. This study has focused on characterizing the sets of faults detected by the techniques and on characterizing the relationships between these sets of faults. The results of the study show that none of the techniques studied is necessarily redundant to any combination of the others. Further results reveal strengths and weakness in the fault detection by the techniques studied and suggest directions for future research.

Shimeall, Timothy J.↗

NASA NTRSDate not supplied

Topographic Quintet: Comparing Five Methods for Measuring Ultra-High Resolution Topography

We compare different methods for collecting ultra-high resolution topography data within an analog planetary, human landing site scale area. Our aim is to investigate the cost and benefits of different 3D terrain mapping techniques, their associated data collection methods, and how their different specifications (e.g., range, spatial resolution, scanning-time, mobility, operating constraints, GPS-Denied operation, etc.) might be applied to landing-site characterization and mission operations. We compare 3D terrain data collected during a field campaign in November 2021 from an outcrop at Kilbourne Hole in southern New Mexico using different Light Detection and Ranging (LiDAR) sensors on the ground and stereo-derived 3D data from framing cameras mounted on small uncrewed aerial systems (sUAS).Our foci for this experiment are ground-based, surveying, and autonomous vehicle-type 3D scanning sensors that might be used for planetary surface exploration from landed assets (e.g., lander, rover, astronaut-mounted sensors, decent imaging, hoppers, or drones).[e.g. 1]This test is not meant to benchmark these scanners against one another, nor provide a recommendation for a specific make or model. Rather, our goal is to quantify time, effort, resolution, and operational trade-offs that are important for selecting a topographic instrument/methodology for a given scope of terrain characterization. Our results indicate that each technique is capable of exceptional quality terrain characterization for planetary exploration and scientific inquiry, but we hypothesize the appropriate technique is highly dependent on the scope of operational specifications and science requirements.

P Whelley↗

NASA NTRS1991

On the Power of Abstract Interpretation

Increasingly sophisticated applications of static analysis place increased burden on the reliability of the analysis techniques. Often, the failure of the analysis technique to detect some information my mean that the time or space complexity of the generated code would be altered. Thus, it is important to precisely characterize the power of static analysis techniques. We follow the approach of Selur et. al. who studied the power of strictness analysis techniques. Their result can be summarized by saying 'strictness analysis is perfect up to variations in constants.' In other words, strictness analysis is as good as it could be, short of actually distinguishing between concrete values. We use this approach to characterize a broad class of analysis techniques based on abstract interpretation including, but not limited to, strictness analysis. For the first-order case, we consider abstract interpretations where the abstract domain for data values is totally ordered. This condition is satisfied by Mycroft's strictness analysis that of Sekar et. al. and Wadler's analysis of list-strictness. For such abstract interpretations, we show that the analysis is complete in the sense that, short of actually distinguishing between concrete values with the same abstraction, it gives the best possible information. We further generalize these results to typed lambda calculus with pairs and higher-order functions. Note that products and function spaces over totally ordered domains are not totally ordered. In fact, the notion of completeness used in the first-order case fails if product domains or function spaces are added. We formulate a weaker notion of completeness based on observability of values. Two values (including pairs and functions) are considered indistinguishable if their observable components are indistinguishable. We show that abstract interpretation of typed lambda calculus programs is complete up to this notion of indistinguishability. We use denotationally-oriented arguments instead of the detailed operational arguments used by Selur et. al.. Hence, our proofs are much simpler. They should be useful for further future improvements.

Reddy, Uday S.↗

NASA NTRS1992

Scattering and radiation analysis of three-dimensional cavity arrays via a hybrid finite element method

A hybrid numerical technique is presented for a characterization of the scattering and radiation properties of three-dimensional cavity arrays recessed in a ground plane. The technique combines the finite element and boundary integral methods and invokes Floquet's representation to formulate a system of equations for the fields at the apertures and those inside the cavities. The system is solved via the conjugate gradient method in conjunction with the Fast Fourier Transform (FFT) thus achieving an O(N) storage requirement. By virtue of the finite element method, the proposed technique is applicable to periodic arrays comprised of cavities having arbitrary shape and filled with inhomogeneous dielectrics. Several numerical results are presented, along with new measured data, which demonstrate the validity, efficiency, and capability of the technique.

Jin, Jian-Ming↗

NASA NTRS1987

Nondestructive evaluation of structural ceramics

A review is presented on research and development of techniques for nondestructive evaluation and characterization of advanced ceramics for heat engine applications. Highlighted in this review are Lewis Research Center efforts in microfocus radiography, scanning laser acoustic microscopy (SLAM), scanning acoustic microscopy (SAM), scanning electron acoustic microscopy (SEAM), and photoacoustic microscopy (PAM). The techniques were evaluated by applying them to research samples of green and sintered silicon nitride and silicon carbide in the form of modulus-of-rupture bars containing seeded voids. Probabilities of detection of voids were determined for diameters as small as 20 microns for microfucus radiography, SLAM, and SAM. Strengths and limitations of the techniques for ceramic applications are identified. Application of ultrasonics for characterizing ceramic microstructures is also discussed.

Klima, Stanley J.↗

NASA NTRS1972

Microbial degradation of parathion

An organism capable of utilizing parathion as the sole carbon and energy source was isolated by enrichment culture techniques. The bacterium was characterized and tentatively classified as Pseudomonas aeruginosa. A pH of 7.0 - 7.5 and temperature of 30 C were found to be optimum for the consumption of parathion. Virtually no oxygen utilization was observed with resting cell suspensions when nonsolubilized parathion was employed. The use of ethanol as solvent for parathion in resting cell studies or preincubation of cells in ethanol obviated this problem and rapid parathion oxidation was demonstrable. Approximately 80% of the parathion consumed by resting cells was present terminally as carbon dioxide. Permeability of the cell to parathion or its metabolites was contingent upon the use of ethanol as either solvent or denaturant. Metabolites were tentatively identified by thin layer chromatography.

Gibson, W. L.↗

NASA NTRS1974

Epitaxial growth of 6H silicon carbide in the temperature range 1320 C to 1390 C

High-quality epitaxial layers of 6H SiC have been grown on 6H SiC substrates with the grown direction perpendicular to the crystal c-axis. The growth was by chemical vapor deposition from methyltrichlorosilane (CH3SiCl3) in hydrogen at temperatures in the range of 1320 to 1390 C. Epitaxial layers up to 80 microns thick were grown at rates of 0.4 microns/min. Attempts at growth on the (0001) plane of 6H SiC substrates under similar conditions resulted in polycrystalline cubic SiC layers. Optical and X-ray diffraction techniques were used to characterize the grown layers.

Will, H. A.↗

NASA NTRS1974

An assessment of transient hydraulics phenomena and its characterization

A systematic search of the open literature was performed with the purpose of identifying the causes, effects, and characterization (modelling and solution techniques) of transient hydraulics phenomena. The governing partial differential equations are presented which were found to be used most often in the literature. Detail survey sheets are shown which contain the type of hydraulics problem, the cause, the modelling, the solution technique utilized, and experimental verification used for each paper. References and source documents are listed and a discussion of the purpose and accomplishments of the study is presented.

Mortimer, R. W.↗

NASA NTRS1977

Particle size and X-ray analysis of Feldspar, Calvert, Ball, and Jordan soils

Pipette analysis and X-ray diffraction techniques were employed to characterize the particle size distribution and clay mineral content of the feldspar, calvert, ball, and jordan soils. In general, the ball, calvert, and jordan soils were primarily clay size particles composed of kaolinite and illite whereas the feldspar soil was primarily silt-size particles composed of quartz and feldspar minerals.

Chapman, R. S.↗

NASA NTRS1978

Doppler lidar processing for atmospheric turbulence measurements

A Doppler lidar is described, its processing methods are characterized, and two alternate techniques are considered. The described system uses a CO2 laser transmitting at 10.6 microns and a bank of narrow band filters for the spectrum analysis. Typical results obtained with this system are presented. The two alternate techniques involve computation of the discrete spectrum by use of the discrete Fourier transform. The first technique involves single-pulse processing and incoherent integration, while the second technique performs coherent processing on the train of received pulses.

Polge, R. J.↗

NASA NTRS1981

The E3 combustors: Status and challenges

The design, fabrication, and initial testing of energy efficient engine combustors, developed for the next generation of turbofan engines for commercial aircraft, are described. The combustor designs utilize an annular configuration with two zone combustion for low emissions, advanced liners for improved durability, and short, curved-wall, dump prediffusers for compactness. Advanced cooling techniques and segmented construction characterize the advanced liners. Linear segments are made from castable, turbine-type materials.

Sokolowski, D. E.↗

NASA NTRS1981

The E3 combustors - Status and challenges

The technology programs for the Energy Efficient Engine (E3) combustors are outlined, status and test results to date are summarized, and present and future challenges indicated. The NASA-sponsored programs, which are being conducted at the General Electric Company and Pratt & Whitney Aircraft, are making important technology advances. Both combustor designs utilize an annular configuration with two-zone combustion for low emissions, advanced liners for improved durability, and short, curved-wall, dump prediffusers for compactness. Advanced cooling techniques and segmented construction characterize the advanced liners in both programs. Liner segments are made from castable, turbine-type materials. At this time, analysis and design activities have been completed; experimental evaluations are progressing. Test results are verifying both design concepts for combustion, cooling, and mechanical integrity. All goals appear capable of being met, with the exception of NO(x).

Sokolowski, D. E.↗

NASA NTRS1981

Evaluation of high temperature structural adhesives for extended service

Eight different Ti-6Al-4V surface treatments were investigated for each of 10 candidate resins. Primers (two for each resin) were studied for appropriate cure and thickness and initial evaluation of bond joints began using various combinations of the adhesive resins and surface treatments. Surface failure areas of bonded titanium coupons were analyzed by electron microscopy and surface chemical analysis techniques. Results of surface characterization and failure analysis are described for lap shear bond joints occurring with adhesive systems consisting of: (1) LARC-13 adhesive, Pasa jell surface treatment; (2) LARC-13 adhesive, 10 volt CAA treatment; (3) PPQ adhesive, 10 volt CAA treatment; and (4) PPQ adhesive, 5 volt CAA treatment. The failure analysis concentrated on the 10,000 hr 505K (450 F) exposed specimens which exhibited adhesive failure. Environmental exposure data being generated on the PPQ-10 volt CAA and the LARC-TPI-10 volt CAA adhesive systems is included.

Hill, S. G.↗

NASA NTRS1983

Tape/head interface study

Existing high energy tapes, high track density heads, and transport guidance techniques were evaluated and characterized to enable these technologies to be employed in future spacecraft recorders with high confidence. The results of these study efforts demonstrated tracking accuracy tape and head density that will support spacecraft recorders with data rates of a minimum of 150 Mbps and storage capacities ranging from 10 to the 10th to 10 to the 11th bits. Seven high energy tapes of either .25 in width, 1.00 in width, or both, were tested. All tapes were tested at the same speed (30 ips) and the same packing density (33 KBI). The performance of all 1 in tapes was considered superior.

Source record↗

NASA NTRS1984

Ultrasonic nondestructive evaluation, microstructure, and mechanical property interrelations

Ultrasonic techniques for mechanical property characterizations are reviewed and conceptual models are advanced for explaining and interpreting the empirically based results. At present, the technology is generally empirically based and is emerging from the research laboratory. Advancement of the technology will require establishment of theoretical foundations for the experimentally observed interrelations among ultrasonic measurements, mechanical properties, and microstructure. Conceptual models are applied to ultrasonic assessment of fracture toughness to illustrate an approach for predicting correlations found among ultrasonic measurements, microstructure, and mechanical properties.

Vary, A.↗

NASA NTRS1985

Characterization of material surfaces exposed to atomic oxygen on space shuttle missions

Material samples prepared for exposure to ambient atomic oxygen encountered during space shuttle flights in low Earth orbit were characterized by the experimental techniques of ELLIPSOMETRY, ESCA, PIXE, and RBS. The first group of samples, which were exposed during the STS-8 mission, exhibited some very interesting results. The second group of samples, which are to be exposed during the upcoming STS-17 mission, have been especially prepared to yield quantitative information on the optical changes, oxygen solution, and surface layer formation on metal films of silver, gold, nickel, chromium, aluminum, platinum, and palladium evaporated onto optically polished silicon wafers.

Fromhold, A. T.↗