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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS2013

Improved Understanding of the Modeled QBO Using MLS Observations and MERRA Reanalysis

The Quasi-Biennial Oscillation (QBO) dominates the variability of the tropical stratosphere on interannual time scales. The QBO has been shown to extend its influence into the chemical composition of this region through dynamical mechanisms. We have started our analysis using the realistic QBO internally generated by the Goddard Earth Observing System Version 5 (GEOS-5) general circulation model coupled to a comprehensive stratospheric and tropospheric chemical mechanism forced with observed sea surface temperatures over the past 33 years. We will show targeted comparisons with observations from NASAs Aura satellite Microwave Limb Sounder (MLS) and the Modern Era Retrospective-Analysis for Research and Applications (MERRA) reanalysis to provide insight into the simulation of the primary and secondary circulations associated with the QBO. Using frequency spectrum analysis and multiple linear regression we can illuminate the resulting circulations and deduce the strengths and weaknesses in their modeled representation. Inclusion of the QBO in our simulation improves the representation of the subtropical barriers and overall tropical variability. The QBO impact on tropical upwelling is important to quantify when calculating trends in sub-decadal scale datasets.

MERRA↗
NASA NTRS1980

Quantitative analysis of autoradiographic image intensification using Thiourea-S35

Photographic images enhanced by the method of Thiourea-S35 autoradiography are evaluated in terms of signal-to-noise ratio, detective quantum efficiency (DQE), and Wiener spectrum analysis using digitized images. It is determined that the original signal-to-noise ratio is not degraded by the intensification process which allows an increase in the practical working DQE as a function of density. These results apply at all spatial frequencies that were tested. The advantage given by autoradiography is the ability to produce usable images from emulsions originally exposed to the low densities corresponding to maximum DQE and movement of faint image densities above the level of the threshold for detection.

Askins, B. S.↗
NASA NTRS1979

A sunspot periodicity and its possible relation to solar rotation

A least-squares power-spectrum analysis of 122 years of Zurich daily sunspot numbers yields a statistically significant peak at a 12.0715 + or - 0.002 day period. This feature of the sunspot spectrum may be associated with the peak at 12.22 days (sidereal) which Dicke (1976) found in his oblateness data, and may be attributable to the sun's core if it rotates at either a 12.0715-day or a 24.1430-day period (synodic).

Knight, J. W.↗
NASA NTRS1981

Airplane wing vibrations due to atmospheric turbulence

The magnitude of error introduced due to wing vibration when measuring atmospheric turbulence with a wind probe mounted at the wing tip was studied. It was also determined whether accelerometers mounted on the wing tip are needed to correct this error. A spectrum analysis approach is used to determine the error. Estimates of the B-57 wing characteristics are used to simulate the airplane wing, and von Karman's cross spectrum function is used to simulate atmospheric turbulence. It was found that wing vibration introduces large error in measured spectra of turbulence in the frequency's range close to the natural frequencies of the wing.

Pastel, R. L.↗
NASA NTRS1980

A sunspot periodicity and the solar rotation

A least squares power spectrum analysis of daily sunspot numbers for the last 122 years yielded a statistically significant peak at 12.0715 plus or minus .002 days period. This feature at 11.685 days (sidereal) of the sunspot spectrum is discussed in relation to the peak at 12.22 days (sidereal) which Dicke found in his oblateness data. The data is attributed to the Sun's core if the core rotates at either 12.0715 days or 24.1430 days period (synodic). It is suggested that spacecraft observations combined with correlative analysis of solar surface features between eastern and western hemispheres could further reveal a basic core periodicity. A Dicke type space oblateness experiment is discussed for providing better photospheric observations than a ground instrument to determine the core periodicity.

Knight, J. W.↗
NASA NTRS1998

Four Years of EUVE Observations of the Bursting Gamma-Ray Emitting Blazar Markarian 421

We present spectral and timing analysis of all the data collected by the Extreme Ultraviolet Explorer Satellite (EUVE) for the bright, nearby BL Lacertae object, Markarian 421, during the four-year period 1994-1997. During these years Mrk 421 has been observed by EUVE 4 times with the Deep-Survey/Spectrograph and 2 times with the imaging telescopes for a total of approximately 1.4 7nillions seconds. From 1993 to 1996 three very bright gamma ray flares were also detected by the Whipple observatory. In 1994 Mrk 421 was observed simultaneously by EUVE (Apr 2-12) and IUE one month before the TeV flare; of the 2 EUVF, observations (Feb 4-7 and Apr 25-May 13) of 1995, the second was part of a multiwavelength campaign that mapped the evolution of the TeV flare. In 1996 we observed Mrk 421 twice simultaneously with XTE: one immediately before (Apr 17-30) and another one (May 10-11) right after the May 7 1996 TeV flare. And finally in 1997 from Feb. 7 to Feb. ll. The total light curve seems to be smoothly varying on the long time-scale while on a shorter time-scale there is evidence of an EUVE flare well correlated to the TeV energy 1995 flare. We have analysed the three spectral data set in an homogenous way using the appropriate calibration data for the off-axis observations and our analysis confirms the presence of the absorption features around approximately 70A, in the entire 1995 dataset and possibly in the 1996 data set. We also show the first power spectrum analysis of the Mrk 421 EUVE lightcurves and a comparison with the power spectra predicted by current theoretical models.

Cagnoni, Ilaria↗
NASA NTRS1985

Spectral shape variation of interstellar electrons at high energies

The high energy electron spectrum analysis has shown that the electron intensity inside the H2 cloud region, or in a spiral arm, should be much lower than that outside it and the observed electron energy spectrum should flatten again at about 1 TeV. In the framework of the leady box model the recently established rigidity dependence of the escape pathlength of cosmic rays would predict a high energy electron spectrum which is flatter than the observed one. This divergence is explained by assuming that the leaky box model can only apply to cosmic ray heavy nuclei, and light nuclei and electrons in cosmic rays may have different behaviors in the interstellar propagation. Therefore, the measured data on high energy electrons should be analyzed based on the proposed nonuniform galactic disk (NUGD) mode.

Tan, L. C.↗
NASA NTRS1985

Quantitative study on dispersion relations of TIDs observed by an HF Doppler array

A quantitative study on the dispersion relation of traveling ionospheric disturbances (TIDs) was performed by using data obtained by an HF Doppler array. Observed data at three stations are digitized continuously with a sampling period of 10 sec. A schematic illustration of a running analysis method is given. Fourier components omega's and their wave vectors k's of the TIDs are calculated from these subset data from three stations by means of the cross-spectrum analysis. Diagrams of horizontal trace velocity V sub ph versus wave period T were also obtained. From these diagrams one can see clear cutoff periods of the internal mode of the atmospheric gravity waves. A morphological classification of the mode of the omega - k and V sub ph - T obtained through one year was performed. The estimation of the horizontal velocity vectors of the thermospheric wind form their dispersion relations was performed also. A key point of the method of obtaining the vectors is to estimate the tilt, in azimuthally different omega - k diagrams, of a resonant branch ascribed to the Brunt oscillations.

Tsutsui, M.↗
NASA NTRS1993

Age and thermochronology of K-feldspars from the Manson Impact Structure

As a contribution to the effort to obtain a precise age for the Manson Impact Structure, we are approaching the problem from a thermo chronological perspective, with the goal of extracting an age from Ar-40/Ar-39 age-spectrum analysis of partially overprinted K-feldspars taken from granitoid clasts. We find that shocked feldspars from Manson generally show a strong overprint in their age spectra, with more than 50 percent of each spectrum being reset. The reset portions of the age spectra correspond to gas lost from very small diffusion domains, and a characteristic of the Manson samples is the very large range in apparent diffusion dimensions that they display, with the smallest domains being some 400 times smaller than the largest domains. It is also noteworthy that the small domains comprise a substantial portion of the volume of the feldspars (50 percent or more). These observations are consistent with the extreme shock experienced by these samples. In detail, the spectra we have measured to date are saddle-shaped and show minimum ages of between 67 and 72 Ma, which we interpret to be maximum estimates for the age of the impact. In the case of one sample (M1-678.3; K-feldspar from a large syenite block located well below the apparent melt-matrix breccia in the M1 borehole), isotope correlation analysis suggests the presence of a non-atmospheric trapped Ar component (Ar-40/Ar-36 of 660 plus or minus 40), and an age of about 65.3 plus or minus 0.5 Ma (2 sigma). Our interpretation of our results is that the shock of impact greatly reduced the diffusion-domain sizes of our samples, making them susceptible to significant Ar loss during heating associated with impact. It appears that while our feldspars were partially open to Ar loss, they equilibrated with a non-atmospheric Ar component, probably related to impact-related degassing of old basement around the impact site.

Zeitler, P. K.↗
NASA NTRS1977

Optimal design and evaluation criteria for acoustic emission pulse signature analysis

Successful pulse recording and evaluation is strongly dependent on the instrumentation system selected and the method of analyzing the pulse signature. The paper studies system design, signal analysis techniques, and interdependences with a view toward defining optimal approaches to pulse signal analysis. For this purpose, the instrumentation system is modeled, and analytical pulses, representative of the types of acoustic emissions to be distinguished are passed through the system. Particular attention is given to comparing frequency spectrum analysis and deconvolution referred to as time domain reconstruction of the pulse or pulse train. The possibility of optimal transducer-filter system parameters is investigated. Deconvolution of a pulse is shown to be a superior approach for transient pulse analysis. Reshaping of a transducer output back to the original input pulse is possible and gives an accurate representation of the generating pulse in the time domain. Any definable transducer and filter system can be used for measurement of pulses by means of the deconvolution method. Selection of design variables for general usage is discussed.

Houghton, J. R.↗
NASA NTRS1981

Solar cycle signal in air temperature in North America - Amplitude, gradient, phase and distribution

The considered investigation was motivated by three factors. One is related to an extension of single-channel MESA to multi-channel by Strand (1977), Morf et al. (1978), and Jones (1978). MESA is a high-resolution signal processing and spectrum analysis technique due to Burg (1975). The considered developments resulted in the discovery of the 11-year solar cycle signal in the change of the length of day by Currie (1980, 1981). They also led Currie (1981) to study the phase spectrum of the 11-year term in height H of sea level. The investigation tries to clarify the phase relations among the involved parameters. The second factor is connected with an application of the linear time domain technique used by Currie (1981) to temperature records to obtain more accurate information regarding the signal amplitude. The third factor of motivation is related to increases in the number of stations available for an analysis, the greater average length of the records, and the more accurate data set.

Currie, R. G.↗
NASA NTRS1991

Adaptive filtering and maximum entropy spectra with application to changes in atmospheric angular momentum

The spectral resolution and statistical significance of a harmonic analysis obtained by low-order MEM can be improved by subjecting the data to an adaptive filter. This adaptive filter consists of projecting the data onto the leading temporal empirical orthogonal functions obtained from singular spectrum analysis (SSA). The combined SSA-MEM method is applied both to a synthetic time series and a time series of AAM data. The procedure is very effective when the background noise is white and less so when the background noise is red. The latter case obtains in the AAM data. Nevertheless, reliable evidence for intraseasonal and interannual oscillations in AAM is detected. The interannual periods include a quasi-biennial one and an LF one, of 5 years, both related to the El Nino/Southern Oscillation. In the intraseasonal band, separate oscillations of about 48.5 and 51 days are ascertained.

Penland, Cecile↗
NASA NTRS2016

On Holo-Hilbert Spectral Analysis: A Full Informational Spectral Representation for Nonlinear and Non-Stationary Data

The Holo-Hilbert spectral analysis (HHSA) method is introduced to cure the deficiencies of traditional spectral analysis and to give a full informational representation of nonlinear and non-stationary data. It uses a nested empirical mode decomposition and Hilbert-Huang transform (HHT) approach to identify intrinsic amplitude and frequency modulations often present in nonlinear systems. Comparisons are first made with traditional spectrum analysis, which usually achieved its results through convolutional integral transforms based on additive expansions of an a priori determined basis, mostly under linear and stationary assumptions. Thus, for non-stationary processes, the best one could do historically was to use the time- frequency representations, in which the amplitude (or energy density) variation is still represented in terms of time. For nonlinear processes, the data can have both amplitude and frequency modulations (intra-mode and inter-mode) generated by two different mechanisms: linear additive or nonlinear multiplicative processes. As all existing spectral analysis methods are based on additive expansions, either a priori or adaptive, none of them could possibly represent the multiplicative processes. While the earlier adaptive HHT spectral analysis approach could accommodate the intra-wave nonlinearity quite remarkably, it remained that any inter-wave nonlinear multiplicative mechanisms that include cross-scale coupling and phase-lock modulations were left untreated. To resolve the multiplicative processes issue, additional dimensions in the spectrum result are needed to account for the variations in both the amplitude and frequency modulations simultaneously. HHSA accommodates all the processes: additive and multiplicative, intra-mode and inter-mode, stationary and nonstationary, linear and nonlinear interactions. The Holo prefix in HHSA denotes a multiple dimensional representation with both additive and multiplicative capabilities.

Huang, Norden E.↗
DOE OSTI2025

Hyperspectral x-ray imaging mapping capabilities for nuclear forensics

Nuclear forensics relies on the integration of complementary signatures to constrain the origins and history of materials. Outcomes benefit from the timeliness and precision of the disparate methods that form typical analysis chains. Sample forms are often either minute in quantity or contain signatures like morphology or composition heterogeneity encoded on a microscale, so many analysis techniques focus on resolving signatures on ever-smaller length scales. The new hyperspectral x-ray imaging (HXI) instrument developed at Los Alamos National Laboratory seeks to improve the information available from scanning electron microscopy (SEM) x-ray spectrum analysis through superior spectral energy resolution vs. typical energy dispersive spectroscopy (EDS) systems in common use in nuclear forensics and other microanalysis fields. Based on arrays of transition-edge sensor (TES) microcalorimeter detectors, this instrument achieves a typical energy resolution of 7 eV full-width at half-maximum (FWHM) at 2 keV, opening new possibilities in trace element detection/analysis and chemical state determination through spectral shape shifts. We present here some of the first applications of the HXI instrument to actinide samples and discuss potential maturation of this nascent technology for future analysis pipelines.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS2002

The Anisotropy of the Microwave Background to l=3500: Mosaic Observations with the Cosmic Background Imager

Using the Cosmic Background Imager, a 13-element interferometer array operating in the 26-36 GHz frequency band, we have observed 40 deg (sup 2) of sky in three pairs of fields, each approximately 145 feet x 165 feet, using overlapping pointings: (mosaicing). We present images and power spectra of the cosmic microwave background radiation in these mosaic fields. We remove ground radiation and other low-level contaminating signals by differencing matched observations of the fields in each pair. The primary foreground contamination is due to point sources (radio galaxies and quasars). We have subtracted the strongest sources from the data using higher-resolution measurements, and we have projected out the response to other sources of known position in the power-spectrum analysis. The images show features on scales approximately 6 feet-15 feet, corresponding to masses approximately 5-80 x 10(exp 14) solar mass at the surface of last scattering, which are likely to be the seeds of clusters of galaxies. The power spectrum estimates have a resolution delta l approximately 200 and are consistent with earlier results in the multipole range l approximately less than 1000. The power spectrum is detected with high signal-to-noise ratio in the range 300 approximately less than l approximately less than 1700. For 1700 approximately less than l approximately less than 3000 the observations are consistent with the results from more sensitive CBI deep-field observations. The results agree with the extrapolation of cosmological models fitted to observations at lower l, and show the predicted drop at high l (the "damping tail").

Pearson, T. J.↗
NASA NTRS1997

Plural-wavelength flame detector that discriminates between direct and reflected radiation

A flame detector employs a plurality of wavelength selective radiation detectors and a digital signal processor programmed to analyze each of the detector signals, and determine whether radiation is received directly from a small flame source that warrants generation of an alarm. The processor's algorithm employs a normalized cross-correlation analysis of the detector signals to discriminate between radiation received directly from a flame and radiation received from a reflection of a flame to insure that reflections will not trigger an alarm. In addition, the algorithm employs a Fast Fourier Transform (FFT) frequency spectrum analysis of one of the detector signals to discriminate between flames of different sizes. In a specific application, the detector incorporates two infrared (IR) detectors and one ultraviolet (UV) detector for discriminating between a directly sensed small hydrogen flame, and reflections from a large hydrogen flame. The signals generated by each of the detectors are sampled and digitized for analysis by the digital signal processor, preferably 250 times a second. A sliding time window of approximately 30 seconds of detector data is created using FIFO memories.

Hall, Gregory H.↗
NASA NTRS1985

CO2 compressor vibration and cause analysis

The operational experience of a large turbine drive carbon dioxide compressor train in a urea plant with capacity of 1620 tons/day is considered. After the initial start-up in 1976, the vibration in the HP cylinder was comparatively serious. The radial vibration reached 4.2 to 4.5 mils and fluctuated around this value. It was attributed to the rotating stall based on the spectrum analysis. Additional return line from the 4th to 4th and higher temperature of the 4th inlet has cured the vibration. Problems are described which were encountered in the operation along with their solutions, and/or improvements.

Ying, Y. L.↗