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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 145 records · Page 8

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NASA NTRS2021

Estimated Ambient Sonic Boom Metric Levels and X-59 Signal-to-Noise Ratios across the USA

NASA is building the X-59 Quiet Supersonic Technology aircraft to produce low noise sonic booms for a series of community noise surveys across the USA. Survey participants will rate their perception of the low-booms from supersonic X-59 flyovers. Several noise metrics are proposed to quantify the noise dose: A-, B-, D-, and E-weighted Sound Exposure Level, Stevens Perceived Level, and Indoor Sonic Boom Annoyance Predictor. Sparse measurements across the survey area will be used to estimate community noise exposure. The level of these low-booms may be comparable to the ambient noise level in some locations, leading to uncertainty in noise exposure estimations. This uncertainty may necessitate increased reliance on sonic boom propagation predictions for exposure estimation. Low-boom signal to ambient noise ratio is one way to quantify uncertainty in measured sonic boom levels. An empirical relationship between A-weighted ambient level and sonic boom metric levels is used in conjunction with the National Park Service’s L50 SPL map to estimate ambient noise levels expressed in terms of sonic boom noise metrics across the USA. These estimates of ambient levels will aid in X-59 community test planning and execution. The signal-to-noise ratio for the undertrack X-59 sonic boom is also estimated, and an example application of these data is presented for comparing potential noise monitor sites prior to a community noise test.

X-59↗

NASA NTRS2021

Risk Assessment Metrics for NASA Fission Reactor Applications

Risk assessment is an important part of many NASA activities. In August 2019, the White House issued NSPM-20, which defines acceptable levels of risk for nuclear launches, but does not prescribe the particular methodologies or metrics that are to be used for comparison to the defined acceptance criteria. There are a variety of metrics that are possible and can be readily generated by a probabilistic risk assessment (PRA). This paper will explore alternative metrics that can be provided, along with some discussion of their characteristics and important factors to consider during a space fission reactor risk analysis.

Probabilistic Risk Assessment↗

NASA NTRS2018

Performance Metrics for the Assessment of Satellite Data Products: An Ocean Color Case Study

Performance assessment of ocean color satellite data has generally relied on statistical metrics chosen for their common usage and the rationale for selecting certain metrics is infrequently explained. Commonly reported statistics based on mean squared errors, such as the coefficient of determination (r2), root mean square error, and regression slopes, are most appropriate for Gaussian distributions without outliers and, therefore, are often not ideal for ocean color algorithm performance assessment, which is often limited by sample availability. In contrast, metrics based on simple deviations, such as bias and mean absolute error, as well as pair-wise comparisons, often provide more robust and straightforward quantities for evaluating ocean color algorithms with non-Gaussian distributions and outliers. This study uses a SeaWiFS chlorophyll-a validation data set to demonstrate a framework for satellite data product assessment and recommends a multimetric and user-dependent approach that can be applied within science, modeling, and resource management communities.

remote sensing↗

NASA NTRS1973

New two-metric theory of gravity with prior geometry

A Lagrangian-based metric theory of gravity is developed with three adjustable constants and two tensor fields, one of which is a nondynamic 'flat space metric' eta. With a suitable cosmological model and a particular choice of the constants, the 'post-Newtonian limit' of the theory agrees, in the current epoch, with that of general relativity theory (GRT); consequently the theory is consistent with current gravitation experiments. Because of the role of eta, the gravitational 'constant' G is time-dependent and gravitational waves travel null geodesics of eta rather than the physical metric g. Gravitational waves possess six degrees of freedom. The general exact static spherically-symmetric solution is a four-parameter family. Future experimental tests of the theory are discussed.

Lightman, A. P.↗

NASA NTRS1974

Solar longitude dependence of some characteristics of type III radio bursts from metric to hectometric wavelengths

Using the observed data for metric and hectometric type III radio bursts, the dependence of burst characteristics on the solar longitude has been examined over a wide frequency range. It is found that there exists and east-west asymmetry for the extension of metric type III bursts into the hectometric wavelength range. In particular, hectometric bursts are rarely observed for solar flares associated with metric bursts east of 60 E solar longitude. Furthermore, for east longitudes, the low-frequency radio observations show a large dispersion in drift time interval.

Sakurai, K.↗

NASA NTRS1975

Growth of metric noise continuum storms and its relation to the source of microwave S-emissions

The relationship between metric noise continuum storms and the S-component of solar microwave emissions is examined by considering the properties of a solar active region and its relation to LF radio burst emissions observed by IMP 6. It is noted that the development of radio noise continuum sources in metric frequencies or less is usually preceded by the appearance of an S-emission source, which is formed in complex sunspot groups such as beta-gamma and gamma types. A model for the development of radio noise continuum sources in metric and decametric frequencies is proposed in which the development of relationships between emissions is closely connected to the growth of magnetic-field lines above associated sunspot groups into complex configurations.

Sakurai, K.↗

NASA NTRS1976

Anisotropic parametrized post-Newtonian gravitational metric field

The anisotropic generalization of the parameterized post-Newtonian (PPN) gravitational metric field is made for the case of theories with energy and momentum conservation laws. Such an anisotropic metric field will generally result in two-tensor or bimetric theories of gravity in an anisotropic universe. New anisotropic 3 x 3 spatial PPN matrices are introduced into the general metric expansion. Earth gravimeter measurements strongly restrict some anisotropies, while anisotropic inertial and gravitational mass for celestial bodies result from other combinations of the PPN matrices.

Nordtvedt, K., Jr.↗

NASA NTRS1982

NASA education briefs for the classroom. Metrics in space

The use of metric measurement in space is summarized for classroom use. Advantages of the metric system over the English measurement system are described. Some common metric units are defined, as are special units for astronomical study. International system unit prefixes and a conversion table of metric/English units are presented. Questions and activities for the classroom are recommended.

Source record↗

NASA NTRS1983

Association between gradual hard X-ray emission and metric continua during large flares

X-ray radiation is used to study coronal phenomena in conjunction with meter wave observations during some large solar flares. It is found that metric flare continua and moving type IV bursts are associated with gradual and long lasting (a few tens of minutes) microwave and hard X-ray emissions. The detailed temporal analysis reveals that although metric and hard X-ray sources are located at very different heights, both kinds of emission result from a common and continuous/repetitive injection of electrons in the corona. The late part of the metric event (stationary type IV burst) is only associated with soft X-ray radiation. This indicates that the mean energy of the radiating electrons is lower during stationary type IV bursts than during the earlier parts of the event.

Klein, L.↗

NASA NTRS1984

Design metrics for maintenance +

Results of a study to develop maintenance metrics based on structural software design characteristics are described. A characteristic metric set suited to explain and predict software maintenance behavior is defined. The maintenance aspects investigated are stability and modifiability. While stability addresses the average number of modules affected per change cause, modifiability characterizes the ease with which changes can be made within each of these modules. Additional interest is dedicated to the difference between characteristic design and implementation metric sets, and to the difference between change behavior during development and maintenance. The development of six software systems and controlled maintenance experiments using these system is examined.

Rombach, H. D.↗

NASA NTRS1985

Application of variable metric methods to structural synthesis

Powell (1977, 1978), Biggs (1972, 1975), and Han (1976, 1977) have developed a class of variable metric methods which create an explicit, quadratic, subproblem which is to be solved for finding a search direction for design improvement. A one-dimensional search is then performed. The present paper has the objective to present this variable metric approach in the context of structural synthesis. The variable metric algorithm is modified for application to the structural synthesis problem. The application of the new procedure is illustrated with the aid of examples, taking into account a 10-bar planar truss, a 17-bar planar tower, and a cantilever beam.

Vanderplaats, G. N.↗

NASA NTRS1986

The relationship of shock-associated kilometric radio emission with metric type II bursts and energetic particles

Shock-associated (SA) events from 1978 to 1982 are compared with metric type II bursts and solar energetic particle (SEP) events. Most metric type II bursts are not obviously associated with SA events at 1980 kHz. Metric type II bursts associated with magnetically well connected flares and SA emission are well correlated with SEP events; those without SA emission are poorly correlated with SEP events. The largest SEP events from flares at any longitude are well correlated with SAs. These results are consistent with the hypothesis that the escaping electrons giving rise to SA emission are accelerated in coronal shocks.

Kahler, S. W.↗

NASA NTRS1988

Node synchronization of viterbi decoders using state metrics

The concept of node synchronization using state metrics is investigated. The branch metrics are integrated over a fixed time interval and the results are compared to the detection threshold. If the threshold is exceeded, the out-of-sync hypothesis is accepted; otherwise, the in-sync hypothesis is accepted. It is shown that the detection threshold can be chosen independent of any particular convolutional code with fixed code rate and constant length if the code has reasonably good bit error rate performance. Three node synchronization schemes are compared: (1) a scheme using the syndrome; (2) a scheme using the frame-sync patterns; and (3) a scheme using the state metrics. At very low signal to noise ratios (SNR), scheme 2 can be faster than scheme 1. For Voyager's rate 1/2 and constraint length 7 convolutional code, this happens for SNRs of less than 0.7 dB. This result is obtained by assuming that the code frame-sync pattern has good aperiodic autocorrelation properties. For a fixed false alarm probability, the sequential detection scheme based on the syndrome is faster than scheme 3 with fixed integration time. A sequential detection technique is needed to improve the speed of scheme 3.

Cheng, U.↗

NASA NTRS1989

Shock-associated kilometric radio emission and solar metric type II bursts

New criteria are used here to select and study the properties of shock-associated (SA) kilometric bursts. Nearly half of all intense metric type II bursts were temporally associated with 1980 kHz emission which was not attributable to metric type III bursts. A quarter of all intense type II bursts are not associated with any significant 1980 kHz emission and another quarter are accompanied by 1980 kHz emission presumed due to type II bursts. The SA bursts are generally not well correlated with microwave flux-density profiles but compare more closely with the most intense and structured parts of the profiles of metric type II bursts. These results imply that the SA emission is due primarily to energetic electrons accelerated at the associated shock.

Kahler, S. W.↗

NASA NTRS1989

Parallel projected variable metric algorithms for unconstrained optimization

The parallel variable metric optimization algorithms of Straeter (1973) and van Laarhoven (1985) are reviewed, and the possible drawbacks of the algorithms are noted. By including Davidon (1975) projections in the variable metric updating, researchers can generalize Straeter's algorithm to a family of parallel projected variable metric algorithms which do not suffer the above drawbacks and which retain quadratic termination. Finally researchers consider the numerical performance of one member of the family on several standard example problems and illustrate how the choice of the displacement vectors affects the performance of the algorithm.

Freeman, T. L.↗

NASA NTRS1990

Assessment of proposed fighter agility metrics

This paper presents the results of an analysis of proposed metrics to assess fighter aircraft agility. A novel framework for classifying these metrics is developed and applied. A set of transient metrics intended to quantify the axial and pitch agility of fighter aircraft is evaluated with a high fidelity, nonlinear F-18 simulation. Test techniques and data reduction method are proposed, and sensitivities to pilot introduced errors during flight testing is investigated. Results indicate that the power onset and power loss parameters are promising candidates for quantifying axial agility, while maximum pitch up and pitch down rates are for quantifying pitch agility.

Liefer, Randall K.↗

NASA NTRS1992

Metric transition

This report describes NASA's metric transition in terms of seven major program elements. Six are technical areas involving research, technology development, and operations; they are managed by specific Program Offices at NASA Headquarters. The final program element, Institutional Management, covers both NASA-wide functional management under control of NASA Headquarters and metric capability development at the individual NASA Field Installations. This area addresses issues common to all NASA program elements, including: Federal, state, and local coordination; standards; private industry initiatives; public-awareness initiatives; and employee training. The concluding section identifies current barriers and impediments to metric transition; NASA has no specific recommendations for consideration by the Congress.

Source record↗

NASA NTRS1993

Specification-based software sizing: An empirical investigation of function metrics

For some time the software industry has espoused the need for improved specification-based software size metrics. This paper reports on a study of nineteen recently developed systems in a variety of application domains. The systems were developed by a single software services corporation using a variety of languages. The study investigated several metric characteristics. It shows that: earlier research into inter-item correlation within the overall function count is partially supported; a priori function counts, in themself, do not explain the majority of the effort variation in software development in the organization studied; documentation quality is critical to accurate function identification; and rater error is substantial in manual function counting. The implication of these findings for organizations using function based metrics are explored.

Jeffery, Ross↗