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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Tomographical imaging using uniformly redundant arrays

An investigation is conducted of the behavior of two types of uniformly redundant array (URA) when used for close-up imaging. One URA pattern is a quadratic residue array whose characteristics for imaging planar sources have been simulated by Fenimore and Cannon (1978), while the second is based on m sequences that have been simulated by Gunson and Polychronopulos (1976) and by MacWilliams and Sloan (1976). Close-up imaging is necessary in order to obtain depth information for tomographical purposes. The properties of the two URA patterns are compared with a random array of equal open area. The goal considered in the investigation is to determine if a URA pattern exists which has the desirable defocus properties of the random array while maintaining artifact-free image properties for in-focus objects.

Cannon, T. M.↗
NASA NTRS1979

Portable device for detection of petit mal epilepsy

A portable device that analyzes the electroencephalogram to determine if petit mal epilepsy waveforms are present is developed and tested. Clinicians should find it useful in diagnosing seizure activity of their patients. The micropower, battery-operated, portable device indicates a seizure has occurred if three criteria are satisfied: (1) frequencies of 2.5-7 Hz, (2) large-amplitude waves, and (3) minimum number of waves per second. Levels and counts are adjustable, thus insuring high reliability against noise artifacts and permitting each subject to be individually fitted. The device has shown promise in giving the patient a possible mechanism of seizure control or suppression.

Smith, R. G.↗
NASA NTRS1980

Pocket ECG electrode

A low noise electrode suited for sensing electrocardiograms when chronically and subcutaneously implanted in a free ranging subject is described. The electrode comprises a pocket shaped electrically conductive member with a single entrance adapted to receive body fluids. The exterior of the member and the entrance region is coated with electrical insulation so that the only electrolyte/electrode interface is within the member, remote from artifact-generating tissue. Cloth straps are bonded to the member to permit the electrode to be sutured to tissue and to provide electrical lead flexure relief.

Lund, G. F.↗
NASA NTRS1979

A microprocessor-based cardiotachometer

The development of a highly accurate and reliable cardiotachometer for measuring the heart rate of test subjects is discussed. It measures heart rate over the range of 30 to 250 beats/minute and gives instantaneous (beat to beat) updates on the system output so that occasional noise artifacts or ectopic beats could be more easily identified except that occasional missed beats caused by switching ECG leads should not cause a change in the output. The cardiotachometer uses an improved analog filter and R-wave detector and an Intel 8080A microprocessor to handle all of the logic and arithmetic necessary. By using the microprocessor, future hardware modifications could easily be made if functional changes were needed.

Donaldson, J. A.↗
NASA NTRS1980

Excursion of vibrating microelectrodes in tissue

The paper deals with a vibrating microelectrode holder consisting of a support rod attached to the cone of a miniature loudspeaker. This holder facilitates a microelectrode penetration into arterial wall tissue, eliminates surface dimpling, and relieves polarographic artifacts believed to be due to tissue compression. The paper presents construction and performance details of the electrode holder, and evaluates the extent of possible damage incurred during such vibration by measuring electrode motion relative to surrounding tissue in an excised segment of femoral artery in the rabbit. It is concluded that under proper vibratory conditions microelectrodes can be easily inserted into the arterial wall with minimum tissue disturbance.

Kanabus, E. W.↗
NASA NTRS1980

Measurements of the sampling volume of an infrared laser doppler velocimeter for the study of feasibility of simultaneous three-dimensional velocity profile mapping

High resolution incoherent mapping of the sampling volume was performed to determine the three dimensional profile of the volume of the beam from which information can be obtained by scattering. The incoherent sampling volume of the infrared laser Doppler velocimeter was found to be heavily dependent upon the configuration of the outgoing laser beam. In general when only half the beam is allowed to focus at the focal plane, the x, y traverses indicate a broader beam with nominal side lobes. However, if the total beam is permitted to impinge on the focal plane there is substantial narrowing of the beam with increased maximum intensity and an increase in side lobes. The double maximum indicated by the coherent sampling volume appears to be an artifact of the scanning process not a fundamental entity of the sampling volume.

Bond, R. L.↗
NASA NTRS1981

An extended classical solution of the droplet growth problem

Problems of applying the classical kinetic theory to the growth of small droplets from vapor are examined. A solution for the droplet growth equation is derived which is based on the assumption of a diffusive field extending to the drop surface. The method accounts for partial thermal and mass accommodation at the interface and the kinetic limit to the mass and heat fluxes, and it avoids introducing the artifact of a discontinuity in the thermal and vapor field near the droplet. Consideration of the environmental fields in spherical geometry utilizing directional fluxes yields boundary values in terms of known parameters and a new Laplace transform integral.

Anderson, B. J.↗
NASA NTRS1980

The magnetic field of Saturn - Further studies of the Pioneer 11 observations

Analysis of magnetic field observations by the Goddard Space Flight Center high-field flux gate magnetometer on the Pioneer 11 spacecraft during Saturn encounter yields estimates of the planetary field. The field is mainly dipolar but rather weaker than expected, with a moment equal to 0.20 G cubic Saturn radii or 4.3 x 10 to the 28th G cu cm, opposite in polarity to earth's. Surprisingly, the field appears to be axially symmetric but with a small (0.04 Saturn radii) offset to the north so that N (S) polar field intensities are 0.6 (0.4) G, respectively. The deduced polar offset appears not to be an artifact of the limited spatial extent of the observations or the presence of fields of external origin. The average stand-off distance of the magnetopause is expected to be 20 Saturn radii, i.e., at the orbit of Titan, so that this largest of solar system satellites is immersed not only in the Saturnian magnetosphere but also at times in its magnetosheath and sometimes even in the interplanetary medium.

Acuna, M. H.↗
NASA NTRS1981

Context sensitive formulations of antenna pattern correction and side lobe compensation for NOSS/LAMMR real time processing

Large antenna multi-channel microwave radiometer (LAMMR) software specifications were written for LAMMR ground processing. There is a need to determine more computationally-efficient antenna temperature correction methods in compensating side lobe contributions especially near continents, islands and weather fronts. One of the major conclusions was that the antenna pattern corrections (APC) processes did not accomplish the implied goals of compensating for the antenna side lobe influences on brightness temperature. A-priori knowledge of land/water locations was shown to be needed and had to be incorporated in a context sensitive APC process if the artifacts caused by land presence is to be avoided. The high temperatures in land regions can severely bias the lower ocean response.

Chin, R. T.↗
NASA NTRS1981

Use of MAGSAT anomaly data for crustal structure and mineral resources in the US midcontinent

While the preliminary magnetic anomaly map for the centra midcontinent is only in the hand-drawn stage, it agrees in broad aspects with the preliminary global MAGSAT map provided by NASA. Because of data evaluation and finer scale averaging, there are more detailed features which hold promise for eventual geological/crustal interpretation. Some current analysis is directed at examining whether a map data feature such as an elongated anomaly or trend, which seems parallel to satellite data tracks, is likely of crustal origin or is an artifact of the data set.

Carmichael, R. S.↗
NASA NTRS1981

A semi-empirical photometric theory of cometary gas and dust production: Application to P/Halley's gas production rates

The semiempirical photometric theory of cometary gas and dust production is recalibrated using UV observations from 14 comets and uniform visual photometry from 8 comets. The calibration is not changed significantly but becomes more secure. The complete theory is presented with all approximations evaluated and explained. Numerical calibration aspects are presented in tables. The theory is applied to P/Halley using a light curve without the artifact caused by the close approach to Earth in 1910. Gas production rates predicted for the 1985/86 apparition are similar to those for 1910.

Newburn, R. L.↗
NASA NTRS1982

Ultrasonic measurement of axial stress

The theory of acoustic propagation in strained media is examined, with particular emphasis on rod (bolt) geometries. The continuous wave (CW) approach is the basis of the study, and the theory is developed from a frequency domain analysis standpoint in order to obtain an applied stress/normalized frequency shift relationship. CW measurements may be influenced by such factors as propagation effects, mode conversion, frequency, material properties, and geometry. After the first loading cycle, axial stress measurements for a preloading with an initial frequency of 4.995 36 MHz dropped to 4.989 19 MHz, indicating a 6.17 kHz change. CW and pseudo-CW ultrasonic techniques are found to be reliable for axial stress measurements, and acoustic attenuation measurements correlated to residual stress fields may possibly involve transducer phase cancellation. It is thus concluded that signal drop is an artifact of the transducer directivity, rather than an actual acoustic power decrease.

Heyman, J. S.↗
NASA NTRS1983

Investigation of radiometric properties of LANDSAT-4 MSS

Two full frames of radiometrically corrected (Type A) LANDSAT-4 MSS data were analyzed digitally and visually for evidence of residual calibration differences between detectors, quantization effects, and other sensor-related artifacts. Both standard statistical and Fourier analysis techniques were employed. Opportunities for coincident coverage by LANDSATS 3 and 4 were identified in the contiguous 48 states. Paired acquisitions for two scenes were obtained and analyzed to establish relationships between signal values from common areas imaged by the two MSS Systems. Initial findings on detector-to-detector differences, coherent noise, and LANDSAT 4 to LANDSAT 3 calibration are summarized. Results show that LANDSAT 4 MSS produces data of generally good quality with dynamic ranges and target responses similar to those of previous sensors.

Rice, D. P.↗
NASA NTRS1983

A study of the temporal and spectral characteristics of gamma ray bursts

Gamma-ray burst data obtained from the ISEE-3 Gamma Ray Burst Spectrometer and the Solar Maximum Mission's Hard X-ray Burst Spectrometer (HXRBS) were analyzed to yield information on burst temporal and spectral characteristics. A Monte Carlo approach was used to simulate the HXRBS response to candidate spectral models. At energies above about 100 keV, the spectra are well fit by exponential forms. At lower energies, 30 keV to 60 keV, depressions below the model continua are apparent in some bursts. The depressions are not instrumental or data-reduction artifacts. The event selection criterion of the ISEE-3 experiment is based on the time to accumulate a present number of photons rather than the photon count per unit time and is consequently independent of event duration for a given burst intensity, unlike most conventional systems. As a result, a significantly greater percentage of fast, narrow events have been detected. The ratio of count rates from two ISEE-3 detectors indicates that bursts with durations or approx. one second have much softer spectra than longer bursts.

Norris, J.↗
NASA NTRS1983

Performance evaluation and geologic utility of LANDSAT 4 TM and MSS scanners

Experiments using artificial targets (polyethylene sheets) to help calibrate and evaluate atmospheric effects as well as the radiometric precision and spatial characteristics of the NS-001 and TM sensor systems were attempted and show the technical feasibility of using plastic targets for such studies, although weather precluded successful TM data acquisition. Tapes for six LANDSAT 4 TM scenes were acquired and data processing began. Computer enhanced TM simulator and LANDSAT 4 TM data were compared for a porphyry copper deposit in Southern Arizona. Preliminary analyses performed on two TM scenes acquired in the CCT-PT format, show the TM data appear to contain a marked increase in geologically useful information; however, a number of instrumental processing artifacts may well limit the ability of the geologist to fully extract this information.

Paley, H. N.↗
NASA NTRS1982

Are the high-latitude torsional oscillations of the sun real

A numerical test is made to determine if the high-latitude torsional wave is generated from the low-latitude torsional pattern as a result of reduction procedures. The results indicate that the high-latitude motions are not an artifact of the analysis, but are true solar features. It is also demonstrated that the one-wave-per-hemisphere torsional oscillation does not result from the reduction procedure. These results place the observations in conflict with the predictions of alpha-omega models of the solar cycle.

Labonte, B. J.↗
NASA NTRS1982

On the interpretation of gamma-ray burst continua and possible cyclotron absorption lines

It is pointed out that most gamma-ray bursts have spectra that are fit by an optically thin thermal bremsstrahlung shape. The small emitting volume implied by the observation of spectral features identified as cyclotron absorption lines from a 10 to the 12th Gauss field is shown to prevent thermal bremsstrahlung from providing sufficient luminosities to account for the observed fluxes unless the optical depth to Compton scattering is large. It is also demonstrated that complicated detector response functions can introduce artifacts that mimic absorption features below 60 keV unless the absolute gain of the detector is established and correctly applied in analysis. Comparing the continuum as observed by the Berkeley/Los Alamos ISEE-3 gamma-ray detector with the continuum observed by the Konus (Mazets et al. 1981) experiments, a lack of agreement is found, suggesting that the gain of one of these experiments may be incorrect.

Fenimore, E. E.↗
NASA NTRS1982

Sunspot time series - Spectrum from square law modulation of the Hale cycle

The spectrum of the sunspot index can be qualitatively accounted for by a very simple time series model which the Hale 22 year cycle dominates; the series is amplitude modulated at the 90 year Gleissberg period with an index of 25%. The square of the modulated Hale cycle reproduces all of the spectral lines of the Zurich sunspot index spectrum, provided that a small offset is included in the Hale carrier. Without this, evidence of the 22 year periodicity disappears. The squaring explains the dominance of the 11 year cycle which is an artifact of the modulation as is the 45 year line. The offset suggests a small relict magnetic field in the sun's core. Lastly Gilliland (1981) finds a radial eigenmode in the sun with period of 76 + or - 8 years suggestive of a physical basis for the Gleissberg modulation.

Sonett, C. P.↗