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At least 1,495 records · Page 83
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Application of signal analysis to cavitation

The diagnostic facilities of the cross power spectrum and the coherence function have been employed to enhance the identification of not only the inception of cavitation, but also its level. Two piezoelectric pressure transducers placed in the downstream chamber of a model spool valve undergoing various levels of cavitation allowed for the use of both functions - the phase angle of the complex cross spectrum and the dimensionless coherence function - to sense clearly the difference between noise levels associated with a noncavitating jet from those once cavitation inception is attained. The cavitation noise within the chamber exhibited quite a regular character in terms of the phase difference between instruments for limited cavitation. Varying cavitation levels clearly illustrated the effect of bubble size on the attendant frequency range for which there was an extremely high coherence or nearly perfect causality.

Martin, C. S.↗
NASA NTRS1985

Space vehicle glow measurements on STS 41-D

A flight experiment using a hand-held, image-intensified spectrographic camera was performed on mission 41-D. The instrument enabled the photographic documentation of the position of the spectral slit on the image to be subjected to spectrographic analysis. Because of this instrument feature, the spectrum of the glow on the Shuttle tail pod could be clearly separated from spectrum of the scattered light from the Orbiter. From the measurements it is clear that the spectrum of the glow is a continuum in the passband of the instrument between 4200 A and 8000 A. The measured spectral resolution of the instrument was 35 A. The scattered light from the Orbiter surfaces distinctly show the components of the earth's airglow at 5577 A and 7620 A. On the same flight material samples were also carried by the Orbiter attached to the Remote Manipulating System arm. These samples were representative of the material overcoatings used on the space telescope. The altitude of the 41-D flight was 290 km, instead of the 220 km which was originally planned for this experiment. The signal to noise ratio in the material glow discrimination experiment was quite low. This made it difficult to draw strong conclusions regarding the glow propensity of the materials. Nevertheless it was clear that polyethylene produces a very weak glow, while most black overcoating materials produce significant glow. MgF2 was also found to produce a relatively intense glow.

Mende, S. B.↗
NASA NTRS1985

Transient response to localized episodic heating in the tropics

It is generally recognized that equatorial disturbances in the lower stratosphere are excited by convective latent heat release associated with the Internal Tropical Convergence Zone (ITCZ). Recently, attention has also focused on tropical convection with regard to extratropical teleconnection patterns. Unlike equatorial waves which are trapped about the equator but propagate vertically, the latter extend well out of the tropics but are barotropic. They have been most widely discussed in connection with long-term climatological features. Both types of disturbances have been examined largely from the standpoint of steady monochromatic forcing, in the latter case zero frequency or time-mean heating. However, tropical convection as revealed by recent geostationary satellite imagery is anything but regular, surely not steady. Much of the heating variance is concentrated spatially within three localized convective centers: Indonesia, the Amazon, and the Congo. Convective activity within these regions undergoes an irregular evolution over the span of a couple of days. It involves a rather broad spectrum of spatial and temporal scales. The analysis of cloud brightness over the Eastern Atlantic and Africa suggests a characteristic time scale of 3-4 days and correlations scales in latitude and longitude of approximately 30 deg.

Salby, M. L.↗
NASA NTRS1991

The spectrum of Saturn from 1990 to 2230/cm - Abundances of AsH3, CH3D, CO, GeH4, NH3, and PH3

An analysis is presented of the abundances and vertical distributions of all known absorbers in the 5-micron spectrum of Saturn, in view of previously unpublished observations, synthetic spectra of each atmospheric constituent, and an atmospheric model for synthesizing Saturn's spectrum in order to make comparisons with observations. The model used encompasses the abundances of all gaseous absorbers, their vertical distributions, clouds, and the thermal and reflected solar components of planetary flux. A coherent understanding is in this way obtained of both the many variables affecting Saturn's 5-micron spectrum and the similarities between Jupiter and Saturn.

Noll, Keith S.↗
NASA NTRS1992

OSSE observations of the Crab pulsar

Preliminary results are presented of the Compton Gamma Ray Observatory Oriented Scintillation Spectrometer Experiment (OSSE) observations of the Crab pulsar. The pulsar energy spectra and light curves are in general agreement with previous observations, validating the OSSE pulsar data acquisition modes and data analysis algorithms. The data suggest that the spectrum of the pulsar varies throughout the light curve. The 'interpulse' region has a slightly flatter spectrum in the approx. 60 to 250 keV region and a slightly steeper spectrum at higher energies than the two main pulses. No evidence was found for any lines in the spectra with a typical sensitivity of about 10(exp -4) photons/sq cm/s.

Ulmer, M. P.↗
NASA NTRS1991

Line-frequency measurements and analysis of N2O between 900 and 4700/cm

The N2O infrared spectrum from 900 to 4700/cm has been studied with a high-resolution Fourier-transform spectrometer. Measurements were made of line frequencies of several N2O isotopes for several ground-state and hot bands. These bands include the 1530-0330, 2330-0330, 0441-0440, 0441-0330, 0531-0330, and 1331-0330 bands of (N-14)2(O-16). Also, perturbation-enhanced transitions in the 0710-0110 and 0730-0110 bands were assigned and measured. The frequencies have been analyzed to obtain a unique set of effective vibration-rotation parameters for each vibrational state. The results obtained from this research are of high accuracy for the ground-state, and the first-excited-state bands of (N-14)2(O-16), in which the computed frequencies derived from the least-squares fits, are known to an absolute uncertainty of only +/-4 x 10 exp -5 for nonperturbed transitions.

Toth, Robert A.↗
NASA NTRS1992

A gravitational lens candidate discovered with the Hubble Space Telescope

Evidence is reported for gravitational lensing of the high-redshift (z = 3.8) quasar 1208 + 101, observed as part of the Snapshot survey with the HST Planetary Camera. An HST V image taken on gyroscopes resolves the quasar into three point-source components, with the two fainter images having separations of 0.1 and 0.5 arcsec from the central bright component. A radio observation of the quasar with the VLA at 2 cm shows that, like most quasars of this redhsift, 1208 + 101 is radio quiet. Based on positional information alone, the probability that the observed optical components are chance superpositions of Galactic stars is small, but not negligible. Analysis of a combined ground-based spectrum of all three components, using the relative brightnesses of the HST image, supports the lensing hypothesis. If all the components are lensed images of the quasar, the observed configuration cannot be reproduced by simple lens models.

Maoz, Dan↗
NASA NTRS1992

Broadband shock associated noise from supersonic jets measured by a ground observer

The theory of broadband shock associated noise from supersonic jets in flight previously developed in the nozzle fixed coordinates is extended to the coordinate system of a stationary ground observer. The extended theory is relevant to community noise and aircraft certification noise prediction. Since the noise source is unaffected by which coordinate system of reference the radiated noise is measured, the same noise source model is retained in the present formulation. Only kinematic arguments are needed in the analysis. A formula for the noise power spectrum as measured by a ground observer is derived. The formula is applicable to hot as well as cold jets. This formula exhibits a form of Doppler shift in the noise spectrum. However, there is no high power convective amplification factor as some other investigators have proposed.

Tam, Christopher K. W.↗
NASA NTRS1992

Relationship between wave energy and free energy from pickup ions in the Comet Halley environment

The free energy available from the implanted heavy ion population at Comet Halley is calculated by assuming that the initial unstable velocity space ring distribution of the ions evolves toward a bispherical shell. Ultimately this free energy adds to the turbulence in the solar wind. Upstream and downstream free energies are obtained separately for the conditions observed along the Giotto spacecraft trajectory. The results indicate that the waves are mostly upstream propagating in the solar wind frame. The total free energy density always exceeds the measured wave energy density because, as expected in the nonlinear process of ion scattering, the available energy is not all immediately released. An estimate of the amount which has been released can be obtained from the measured oxygen ion distributions and again it exceeds that observed. The theoretical analysis is extended to calculate the k spectrum of the cometary-ion-generated turbulence.

Huddleston, D. E.↗
NASA NTRS1994

Steps toward determination of the size and structure of the broad-line region in active galactic nuclei. 5: Variability of the ultraviolet continuum and emission lines of NGC 3783

We report on the results of intensive ultraviolet spectral monitoring of the Seyfert 1 galaxy NGC 3783. The nucleus of NGC 3783 was observed with the International Ultraviolet Explorer satellite on a regular basis for a total of 7 months, once every 4 days for the first 172 days and once every other day for the final 50 days. Significant variability was observed in both continuum and emission-line fluxes. The light curves for the continuum fluxes exhibited two well-defined local minima or 'dips,' the first lasting is less than or approximately 20 days and the second is less than or approximately 4 days, with additional episodes of relatively rapid flickering of approximately the same amplitude. As in the case of NGC 5548 (the only other Seyfert galaxy that has been the subject of such an intensive, sustained monitoring effort), the largest continuum variations were seen at the shortest wavelengths, so that the continuum became 'harder' when brighter. The variations in the continuum occurred simultaneously at all wavelengths (delta(t) is less than 2 days). Generally, the amplitude of variability of the emission lines was lower than (or comparable to) that of the continuum. Apart from Mg II (which varied little) and N V (which is relatively weak and badly blended with Ly(alpha), the light curves of the emission lines are very similar to the continuum light curves, in each case with a small systematic delay or 'lag.' As for NGC 5548, the highest ionization lines seem to respond with shorter lags than the lower ionization lines. The lags found for NGC 3783 are considerably shorter than those obtained for NGC 5548, with values of (formally) approximately 0 days for He II + O III), and approximately 4 days for Ly(alpha) and C IV. The data further suggest lags of approximately 4 days for Si IV + O IV) and 8-30 days for Si III + C III). Mg II lagged the 1460 A continuum by approximately 9 days, although this result depends on the method of measuring the line flux and may in fact be due to variability of the underlying Fe II lines. Correlation analysis further shows that the power density spectrum contains substantial unresolved power over timescales of is less than or approximately 2 days, and that the character of the continuum variability may change with time.

Reichert, G. A.↗
NASA NTRS1999

Capella: Structure and Abundances

This grant covers the analysis of ASCA spectra of the cool star binary system Capella. This project has also required the analysis of simultaneous EUVE data. The ASCA spectrum of Capella could not be fit with standard models; by imposing models based on strong lines observed with EUVE, a problem wavelength region was identified. Correcting the problem required calculations of atomic collision strengths of higher principal quantum number than had ever been calculated, resulting in a paper in process by Liedahl and Brickhouse. With these new models applied to the ASCA spectrum, better fits were obtained. While solar abundance ratios are generally consistent with the ASCA data, the ratio of Ne/Fe is three to four times lower than solar photospheric values. Whether there is a general First Ionization Potential (FIP) effect or a specific neon anomaly cannot be determined from these data. Detailed discussion has been provided to NASA in the most recent annual report (1997). Two poster presentations have been made regarding modeling requirements. A substantial paper is in the final revision form, following review by six co-authors. The results of this work have wide implications, since the newly calculated emission lines almost certainly contribute to other problems in fitting not only other stellar spectra, but also composite supernova remnants, galaxies, and cooling flow clusters of galaxies. Furthermore, Liedahl and Brickhouse have identified other species for which lines of a similar nature (high principal quantum number) will contribute significant flux. For moderate resolution X-ray spectra, lines left out of the models in relatively isolated bands, will be attributed to continuum flux by spectral fitting engines, causing errors in line-to-continuum ratios. Thus addressing the general theoretical problem is of crucial importance.

Brickhouse, Nancy S.↗
NASA NTRS2003

On the Confidence Limit of Hilbert Spectrum

Confidence limit is a routine requirement for Fourier spectral analysis. But this confidence limit is established based on ergodic theory: For stationary process, temporal average equals the ensemble average. Therefore, one can divide the data into n-sections and treat each section as independent realization. Most natural processes in general, and climate data in particular, are not stationary; therefore, there is a need for the Hilbert Spectral analysis for such processes. Here ergodic theory is no longer applicable. We propose to use various adjustable parameters in the shifting processes of the Empirical Mode Decomposition (EMD) method to obtain an ensemble of Intrinsic Mode Function 0 sets. Based on such an ensemble, we introduce a statistical measure in. a form of confidence limits for the Intrinsic Mode Functions, and consequently, the Hilbert spectra. The criterion of selecting the various adjustable parameters is based on the orthogonality test of the resulting M F sets. Length-of-day data from 1962 to 2001 will be used to illustrate this new approach. Its implication in climate data analysis will also be discussed.

Huang, Norden↗
NASA NTRS2004

The Composition and Physical Structure of the Io Torus and Atmosphere

Generally speaking the goal of the research was to provide detailed spectral analysis of a Hopkins Ultraviolet Telescope EUV/FUV spectrum of the Io plasma torus. The specific research tasks outlined to achieve this goal were: Line identifications and brightnesses. Verify line identifications with independent data sets. Simple physical modeling to derive ne, ni, Te. Determine neutral source rates. Determine implications of minor species abundances for Io processes. Determine spatial structure from HUT data.

McGrath, Melissa↗
NASA NTRS2005

XMM-Newton, RXTE, and Radio Observations of CYGNUS X-1

XMM-Newton observations of this target were not made successfully until October 2004, due to problems of high background and instrumental flaring in the prior observability windows. Processed data for analysis was delivered a few months after the observations. Thus, work on these observations is beginning now, in the spring of 2005. A preliminary analysis of these observations reveals a complex spectrum, with relativistic emission line features. Detailed modeling and interpretation of this data will be completed over several months.

Miller, Jon↗
NASA NTRS2005

Time Resolved Spectroscopy of Eclipsing Polars

No changes have been made since the last annual progress report was submitted in conjunction with a unilateral NCX. Dr. Barrett was affected by an STScI Reduction in Force (RIF). He is now employed by the Johns Hopkins University and plans to continue his research there. No expenses have been charged to this grant, however the FUSE data for the eclipsing polar V1432 Aql has been received and processed using CALFWSE v3.0.6. The resulting summed spectrum has been used for a preliminary analysis of the interstellar absorption towards V1432 Aql. We find a hydrogen column density of less than 1.5e21 cm^-2. We have used this result in the paper "X-Ray Emission and Optical Polarization of V1432 Aquilae: An Asynchronous Polar" to fix the hydrogen column density in the soft (<0.5 keV) X-ray band when analyzing the XMM-Newton spectra of this polar. This has enabled us to find an accurate temperature for the blackbody component of 88+/-2 eV, which is significantly higher than that of other polars (20 - 40 eV). We hope to complete our analysis of the phase-resolved emission line spectra of V1432 Aql and to prepare the results for publication in a refereed journal. We hope to begin work on this star within the next few months.

Barrett, Paul↗
NASA NTRS2000

The intensities of methane in the 3-5 mu m region revisited

The analysis of the linestrengths of the infrared spectrum of methane (12 and 13) in the 3-5 mu m region has been revisited onthe basis of new measurements from Fourier transform spectra recorded at Kitt Peak under various optical densities.

Methane High resolution Infrared Absolute intensit↗
NASA NTRS2001

Non-invasive glucose monitor

A non-invasive method for determining blood level of an analyte of interest, such as glucose, comprises: generating an excitation laser beam (e.g., at a wavelength of 700 to 900 nanometers); focusing the excitation laser beam into the anterior chamber of an eye of the subject so that aqueous humor in the anterior chamber is illuminated; detecting (preferably confocally detecting) a Raman spectrum from the illuminated aqueous humor; and then determining the blood glucose level (or the level of another analyte of interest) for the subject from the Raman spectrum. Preferably, the detecting step is followed by the step of subtracting a confounding fluorescence spectrum from the Raman spectrum to produce a difference spectrum; and determining the blood level of the analyte of interest for the subject from that difference spectrum, preferably using linear or nonlinear multivariate analysis such as partial least squares analysis. Apparatus for carrying out the foregoing method is also disclosed.

Lambert, James L.↗
NASA NTRS2003

Assessing blood brain barrier dynamics or identifying or measuring selected substances or toxins in a subject by analyzing Raman spectrum signals of selected regions in the eye

A non-invasive method for analyzing the blood-brain barrier includes obtaining a Raman spectrum of a selected portion of the eye and monitoring the Raman spectrum to ascertain a change to the dynamics of the blood brain barrier. Also, non-invasive methods for determining the brain or blood level of an analyte of interest, such as glucose, drugs, alcohol, poisons, and the like, comprises: generating an excitation laser beam (e.g., at a wavelength of 600 to 900 nanometers); focusing the excitation laser beam into the anterior chamber of an eye of the subject so that aqueous humor, vitreous humor, or one or more conjunctiva vessels in the eye is illuminated; detecting (preferably confocally detecting) a Raman spectrum from the illuminated portion of the eye; and then determining the blood level or brain level (intracranial or cerebral spinal fluid level) of an analyte of interest for the subject from the Raman spectrum. In certain embodiments, the detecting step may be followed by the step of subtracting a confounding fluorescence spectrum from the Raman spectrum to produce a difference spectrum; and determining the blood level and/or brain level of the analyte of interest for the subject from that difference spectrum, preferably using linear or nonlinear multivariate analysis such as partial least squares analysis. Apparatus for carrying out the foregoing methods are also disclosed.

Lambert, James L.↗