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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

A Patched-Grid Algorithm for Complex Configurations Directed Towards the F/A-18 Aircraft

A patched-grid algorithm for the analysis of complex configurations with an implicit, upwind-biased Navier-Stokes solver is presented. Results from both a spatial-flux and a time-flux conservation approach to patching across zonal boundaries are presented. A generalized coordinate transformation with a biquadratic geometric element is used at the zonal interface in order to treat highly stretched viscous grids and arbitrarily-shaped zonal boundaries. Applications are made to the F-18 forebody-strake configuration at subsonic, high-alpha conditions. Computed surface flow patterns compare well with ground-based and flight-test results; the large effect of Reynolds number on the forebody flow-field is shown.

High alpha research vehicle↗
NASA NTRS1986

Correcting observed stellar Lyman alpha profiles for the effects of interstellar absorption and geocoronal emission

Techniques to compensate for interstellar absorption and geocoronal emission in IUE studies of late stars atmospheres were developed. Thus it is possible to determine the Lyman alpha flux from nearby cool stars using the low-resolution spectra in the IUE archives. The accuracy of such a procedure depends fundamentally upon the assumptions regarding the shape of the intrinsic profile and the density and velocity structure of the local interstellar medium, not upon measurement uncertainties of the low-resolution spectra. Geocoronal emission and saturated spectra are fatal only to a one-dimensional spectral analysis. When both the spatial and the spectral dimensions are considered, the observed Lyman alpha flux can be recovered.

Neff, J. E.↗
NASA NTRS1990

Application of a patched-grid algorithm to the F/A-18 forebody-leading-edge extension configuration

A patched-grid algorithm for the analysis of complex configurations with an implicit, upwind-biased Navier-Stokes solver is presented. Results from both a spatial-flux and a time-flux conservation approach to patching across zonal boundaries are presented. A generalized coordinate transformation with a biquadratic geometric element is used at the zonal interface in order to treat highly stretched viscous grids and arbitrarily shaped zonal boundaries. Applications are made to the F/A-18 forebody-Ieading-edge extension configuration at subsonic, high-alpha conditions. Computed surface flow patterns compare well with ground-based and flight-test results; the large effect of Reynolds number on the forebody flowfield is shown.

Leading edge extension↗
NASA NTRS1992

The kinematics of the extended gas in the Seyfert galaxy NGC 3516

Long-slit spectroscopy of the extended gas in the Seyfert galaxy NGC 3516 reveals considerable substructure in the narrow emission lines with several kinematically distinct components visible in H-alpha and N II lambda 6583. The velocity measurements cover almost all of the 3 kpc scale, Z-shaped emission-line structure seen in narrow-band images and suggest that a significant rotational component is present. At large radii, strong deviations from this rotation are observed, indicating that a radial component of motion to the gas is also required to adequately describe the velocity field. There is a clear antisymmetry in these deviations with the velocities being blueshifted with respect to 'normal' galactic rotation on the southwest side of the nucleus and redshifted with respect to it on the northeast side. Although several models can be invoked to explain the observed velocities, the symmetries in the kinematics and emission-line morphology are most easily explained by a bent bipolar mass outflow from the nucleus. In this simple model, gas is ejected out of the plane of the stellar disk and is then slowed by gravitational forces. As the gas trajectory begins to bend, significant velocity deviations are produced. These observations provide some of the best kinematic evidence for mass outflow, although indirect arguments suggest they may be a common feature in many Seyfert galaxies.

Mulchaey, John S.↗
NASA NTRS1994

Size distribution and scattering phase function of aerosol particles retrieved from sky brightness measurements

Ground-based measurements of the solar transmission and sky radiance in a horizontal plane through the Sun are taken in several geographical regions and aerosol types: dust in a desert transition zone in Israel, sulfate particles in Eastern and Western Europe, tropical aerosol in Brazil, and mixed continental/maritime aerosol in California. Stratospheric aerosol was introduced after the eruption of Mount Pinatubo in June 1991. Therefore measurements taken before the eruption are used to analyze the properties of tropospheric aerosol; measurements from 1992 are also used to detect the particle size and concentration of stratospheric aerosol. The measurements are used to retrieve the size distribution and the scattering phase function at large scattering angles of the undisturbed aerosol particles. The retrieved properties represent an average on the entire atmospheric column. A comparison between the retrieved phase function for a scattering angle of 120 deg, with phase function predicted from the retrieved size distribution, is used to test the assumption of particle homogeneity and sphericity in radiative transfer models (Mie theory). The effect was found to be small (20% +/- 15%). For the stratospheric aerosol (sulfates), as expected, the phase function was very well predicted using the Mie theory. A model with a power law distribution, based on the spectral dependence of the optical thickness, alpha, cannot estimate accurately the phase function (up to 50% error for lambda = 0.87 microns). Before the Pinatubo eruption the ratio between the volumes of sulfate and coarse particles was very well correlated with alpha. The Pinatubo stratospheric aerosol destroyed this correlation. The aerosol optical properties are compared with analysis of the size, shape, and composition of the individual particles by electron microscopy of in situ samples. The measured volume size distribution before the injection of stratospheric aerosol consistently show two modes, sulfate particles with r(sub m) less than 0.2 microns and coarse paritcles with r(sub m) greater than 0.7 microns. The 'window' in the tropospheric aerosol in this radius range was used to observe a stable stratospheric aerosol in 1992, with r(sub m) approximately 0.5 microns. A combination of such optical thickness and sky measurements can be used to assess the direct forcing and the climatic impact of aerosol. Systematic inversion for the key aerosol types (sulfates, smoke, dust, and maritime aerosol) of the size distribution and phase function can give the relationship between the aerosol physical and optical properties that can be used to compute the radiative forcing. This forcing can be validated in dedicated field experiments.

Kaufman, Y. J.↗
NASA NTRS1995

Modeling and numerical simulation of microwave pulse propagation in air breakdown environment

It is shown that ionization occurs wherever the field intensity of the pulse exceeds the local breakdown threshold field of the background air. The produced plasma then attenuates the pulse and gives rise to a tail erosion phenomenon that plays the primary role in limiting the energy transfer of the pulse from source to destination. A theoretical model describing the propagation of an intense microwave pulse in an air breakdown environment is developed that includes the possible focusing effect introduced by either using phase array antennas or the other arrangements. The self-consistent description of the propagation process is provided by a set of two modal equations. These include a continuity equation (Poynting's equation) for the energy density of the pulse and a rate equation of the electron density. A forward wave approximation is used to simplify Poynting's equation, and a semiempirical formula is used for the ionization frequency, nu(sub i). This frequency provides the coupling between the two modal equations, and is used to express the electron rate equation explicitly. In terms of the relevant parameters of the atmosphere, these two equations are normalized for numerical analysis of pulse propagation in the atmosphere. The dependencies of the propagation characteristics of the pulse on intensity, frequency, width, and shape of the pulse are determined. The numerical simulations lead to a useful empirical relation p(exp 3)w = alpha = constant, where p and w are the incident power and width of the pulse and alpha depends on the percentage of pulse energy transferred from the source point to a destined position. The density distribution of the pulse's self-generated plasma is also evaluated. The results also show that for ionization caused by a single unfocused microwave pulse transmitted upwards from the ground, the maximum electron density produced at, for example, 50 km altitude is limited by the tail erosion effect to below 10(exp 6) cm(exp -3). Repetitive pulse and focused beam approaches are also examined. Both approaches can increase the maximum electron density by no more than an order of magnitude. A scheme using two obliquely propagating pulses intersecting at the destined height, e.g. 50 km, is considered. It is shown that the electron density generated at the lowest intersecting position can easily reach a value of 6.6 x 10(exp 8) cm(exp -3), which is considered to be high enough for artificial ionospheric mirror (AIM) application.

Kim, J.↗
NASA NTRS1996

Spectral Irradiance Calibration in the Infrared: 3-35 microns Spectra of Three Southern Standard Stars - Part 6

We present three new absolutely calibrated continuous stellar spectra from 3 to 35 microns, constructed as far as possible from actual observed spectral fragments taken from the Kuiper Airborne Observatory (KAO), and the IRAS Low Resolution Spectrometer (LRS). These stars- alpha(sup 1) Cen, alpha TrA, and epsilon Car-augment our previous archive of complete absolutely calibrated spectra for northern K and M giants. All these spectra have a common calibration pedigree. The wavelength coverage is ideal for calibration of many existing and proposed ground-based, airborne, and satellite sensors. KAO and IRAS data in the 15-30 micron range suggest that the spectra of cool giants are close to Rayleigh-Jeans slopes. Our observations of alpha(sup 1) Cen, absolutely calibrated via our adopted Sirius model, indicate an angular diameter in very good agreement with values in the literature, demonstrating 'closure' of the set of spectra within our absolute framework. We compare our observed alpha(sup 1) Cen spectrum with a published grid of theoretical models from Kurucz, and adopt a plausible theoretical shape, that fits our spectrum, as a secondary reference spectrum in the southern sky.

Cohen, Martin↗
NASA NTRS1973

Estimation of aerodynamics for slender bodies alone and with lifting surfaces at alpha's from 0 deg to 90 deg.

Expressions are derived, according to a method developed by the author (1972), for bodies in which the cross-sectional shape (but not necessarily the area) is constant along the longitudinal axis. For the more general case of a body alone or with lifting surfaces where the cross-sectional shape varies along the length, a similar procedure is suggested. The specific case for an elliptic cone with a triangular wing is considered, and formulas for winged elliptic cross sections are developed. For the limited test conditions shown, the agreement between computed and experimental results is very good.

Jorgensen, L. H.↗
NASA NTRS1978

Reflection spectra and magnetochemistry of iron oxides and natural surfaces

The magnetic properties and spectral characteristics of iron oxides are distinctive. Diagnostic features in reflectance spectra (0.5 to 2.4 micron) for alpha Fe2O3, gamma Fe2O3, and FeOOH include location of Fe3(+) absorption features, intensity ratios at various wavelengths, and the curve shape between 1.2 micron and 2.4 micron. The reflection spectrum of natural rock surfaces are seldom those of the bulk rock because of weathering effects. Coatings are found to be dominated by iron oxides and clay. A simple macroscopic model of rock spectra (based on concepts of stains and coatings) is considered adequate for interpretation of LANDSAT data. The magnetic properties of materials associated with specific spectral types and systematic changes in both spectra and magnetic properties are considered.

Wasilewski, P.↗
NASA NTRS1982

Room-temperature mercuric iodide spectrometry for low-energy X-rays

A discussion of the limits of energy resolution in different energy ranges is given. The energy resolution of a spectrometer is analyzed in terms of the parameters characterizing the crystal, the detector, and the amplification electronics. A high-resolution room-temperature HgI2 spectrometry system was used to measure low-energy X-ray fluorescence spectra. For the MgK-alpha X-ray line the measured resolution was 245 eV (fwhm); the electronic noise linewidth of the system was 225 eV. Alpha-particles were used to excite X-ray fluorescence from low-Z elements separately or in combination. The shape of the photopeaks in the spectra is discussed.

Kusmiss, J. H.↗
NASA NTRS1985

X-ray spectrum and variability of 3C 120

The X-ray luminosity of 3C 120 is variable by a factor of 2.5 on time scales of days to months. The spectral slope of the 2-10 keV X-rays changes systematically in the sense that the higher intensity states are steeper. Simple power laws fitted to the data are consistent with an energy index alpha of 0.51 + or - 0.13 at minimum intensity and 0.83 + or - 0.03 at maximum, with a continuous variation in between. A more complicated spectral shape cannot be ruled out, but changes in absorbing column density alone cannot explain the data. The results are interpreted in terms of beamed synchrotron emission from a relativistic jet, a model which has been invoked previously for the spectra of BL Lac objects. The spectral variability is in marked contrast to the behavior of 3C 273, another superluminal source in which the X-ray spectral index is constant to a high degree of accuracy despite variability in time scales and amplitudes which are quite similar to those of 3C 120. The difference may be due to the degree of beaming of the respective core components. Another model which is consistent with the data involves thermal emission from isothermal shocks in a hot (approximately 10 to the 8th K) medium. Thermal Compton and spherical accretion X-ray source models do not reproduce the correct behavior of alpha versus flux.

Halpern, J. P.↗
NASA NTRS1985

The optical structure of the central core in the peculiar supernova remnant CTB 80

Deep and high resolution H-alpha + forbidden N II, O III, and red continuum interference-filter images of the bright central radio core of the supernova remnant CTB 80 are presented. These photographs reveal a surprisingly filamentary structure not visible from previous imaging and indicate considerable morphological differences between forbidden O III and H-alpha + forbidden N II emission regions. The H-alpha + forbidden N II filaments appear elongated in the E-W direction like that of the radio emission plateau surrounding the central core. The forbidden O III emission is much smaller in angular size but matches well the position, shape and size of the core's 6 cm radio emission. Also detected are the two possible optical counterparts reported by Blair and Schild (1984) to the remnants' X-ray point source and it is noted that both may have coincident H-alpha + forbidden N II emission.

Fesen, R. A.↗
NASA NTRS1995

A new criterion for bar-forming instability in rapidly rotating gaseous and stellar systems. 2: Nonaxisymmetric form

We have previously introduced the parameter alpha as an indicator of stability to m = 2 nonaxisymmetric modes in rotating, self-gravitating, axisymmetric, gaseous (alpha less than or approximately equal to 0.34) and stellar (alpha less than or approximately equal to 0.25) systems. This parameter can be written as alpha = (ft/2)(exp 1/2), where t is defined as T/(absolute value of W), T is the total rotational kinetic energy, W is the total gravitational potential energy, and f is a function characteristic of the topology/connectedness and the geometric shape of a system. In this paper, we extend the stability criterion to nonaxisymmetric equilibrium systems by determining empirically the appropriate form of the function f for ellipsoids and elliptical disks and cylinders. We test the validity of this extension of the stability indicator alpha by considering its predictions for previously published, gaseous and stellar, nonaxisymmetric models. The formulation and critical values account accurately for the stability properties of m =2 modes in gaseous Riemann S-type ellipsoids (including the Jacobi and Dedekind ellipsoids) and elliptical Riemann disks as well as in stellar elliptical Freeman disks and cylinders: all these systems are dynamically stable except the stellar elliptical Freeman disks that exhibit a relatively small region of m = 2 dynamical instability. A partial disagreement in the case of stellar Freeman ellipsoids in maximum rotation may be due to the fact that the region of instability has not been previously determined with sufficient accuracy.

Christodoulou, Dimitris M.↗
NASA NTRS1992

The kinematics of the molecular gas in Centaurus A

The CO (2-1) emission along the inner dust lane of Centaurus A, observed with the Caltech Submillimeter Observatory on Mauna Kea, shows the molecular gas to be in a thin disk, with a velocity dispersion of only about 10 km/s. The observed line profiles are broadened considerably due to beam smearing of the gas velocity field. The profile shapes are inconsistent with planar circular and noncircular motion. However, a warped disk in a prolate potential provides a good fit to the profile shapes. The morphology and kinematics of the molecular gas is similar to that of the ionized material, seen in H-alpha. The best-fitting warped disk model not only matches the optical appearance of the dust lane but also agrees with the large-scale map of the CO emission and is consistent with H I measurements at larger radii.

Quillen, A. C.↗
NASA NTRS1995

The interstellar disk-halo connection in the spiral galaxy NGC 3079

We discuss the morphology and excitation of ionized gas in the nearby Sc galaxy NGC 3079. The almost edge-on orientation is ideal for studying the vertical structure of the gaseous disk, and especially the diffuse ionized medium (DIM) found between the bright H II regions. We used the Hawaii Imaging Fabry-Perot Interferometer (HIFI) to map 150,000 H-alpha + (N II) lambda lambda 6548, 6583 emission-line profiles across the entire disk, with resolution 70 km/s at subarcsecond steps, down to a flux level of approximately 10(exp -17) ergs/s/sq cm (EM approximately equal to 4 cm(exp -6) pc). The DIM contributes approximately 30% of the total disk H-alpha emission within a radius of 10 kpc. The DIM has broader emission lines and larger (N II) H-alpha flux ratios than the adjacent H II regions. Within a radius of 5 kpc, we find that the X-shaped filaments reported in previous studies emerge from the inner (R approximately equal to 1.5 kpc) disk, and rise more than 4 kpc above the disk plane. The morphology, kinematics, and excitation of the filaments suggest that they form a biconic interface between the undisturbed disk gas, and gas entrained in the wide-angle outflow. The DIM beyond 5 kpc radius is more vertically extended than the thick ionized disk detected in our Galaxy and in a few nearby edge-on systems. After correcting for dust, the vertical profile of this DIM has an exponential scale height of about 1.1 kpc, similar to that of the H I disk. The (N II) lambda 6538/H-alpha flux ratio of the DIM increases monotonically with vertical height, reaching unity for absolute value of z greater than or approximately equal to 2.5 kpc. The flux required to keep the DIM ionized at R = 8 kpc is similar to that near the solar circle of our Galaxy. Highly dilute radiation from O stars in the galactic plane probably maintains the DIM. The total mass of the DIM is of order 10(exp 8) - 10(exp 9) solar mass, representing less than 1% of the total dynamical mass of NGC 3079. Mechanical energy from intense star formation in the disk probably lifts the DIM above the disk. The several bubbles and filaments within 1 kpc of the disk plane is direct evidence for gas flow between the disk and halo.

Veilleux, Sylvain↗
NASA NTRS2003

Asymmetric Stokes-V Profiles at the Penumbral Boundary of a Sunspot

We present the spectropolarimetric measurements of a sunspot in the active region NOAA 6958 (15S03W), situated near the central meridian disk passage. The follower polarity sunspot was somewhat symmetrically round shaped with an elongated penumbra. There were several opposite polarity magnetic elements at, and beyond the penumbral boundary. The H-alpha images of the sunspot show the bright emission regions near the penumbral boundary towards the sun-center, which was of opposite polarity with respect to the main spot. The net-circular polarization (NCP) map shows that NCP is negative in the inner part of the spot and positive at the penumbral boundary and near the H-alpha plage. The Doppler velocities were determined by measuring the center-of-gravity (COG) of the Stokes-I profile and zero-crossing (ZC) wavelength of the Stokes-V profiles. The COG velocity map in general agrees with the Evershed flow. In addition, it shows the up flow in the penumbral region. The ZC velocities show the strong down flow at the penumbral boundary. Double-lobed Stokes-V profiles are observed at the locations, where the penumbral fibrils terminate coinciding the H-alpha plage. The Double lobed profiles had an unshifted component similar to the Stokes-V profiles of the sunspot penumbra and a shifted component with a velocity of about 5 km/s. The amplitude of the second component increases along the penumbral fibril as a function of the distance from the center of the sunspot. In this paper we discuss the role of emerging flux in generating the observed double lobed profiles. Based on our present observations, we propose to observe with the Solar-B Spectropolarimeter for understanding the nature of emerging flux near the sunspots.

Choudhary, Debi Prasad↗
DOE OSTI2021

Actinide in Air (Rn-Progeny Rejected) Alpha Spectroscopy With Tensioned Metastable Fluid Detectors

Here, this article discusses outcome of research for deriving a methodology and apparatus for ascertaining for the presence of ultratrace-level actinides in air from their alpha emission signatures, while remaining blind to the relatively large (1000× higher activity) alpha emissions from Rn-progeny. Apparatus and techniques were developed to collect and characterize alpha-emitting nuclides of Rn-progeny and actinides in air on a polycarbonate 3 μm pore size continuous air monitor (CAM) filter. A wet-chemistry approach was developed and validated for successfully separating the Rn-progeny alpha emitting isotopes of Po-214 and Po-218, while extracting the actinides (U, Pu, Am) in a fluid mixture that is suitable for conduct of alpha spectroscopy with a centrifugally tensioned metastable fluid detector (CTMFD). The resulting α-TMFD technology was compared against the state-of-art “Alpha-Sentry™” Continuous Air Monitor (CAM) system commonly utilized world-wide. Results indicate that the α-TMFD technology can potentially offer complementary and superior performance in multiple performance categories, and ∼18× improvement in the time to detect (e.g., at 0.02 derived air concentration (DAC) within ∼3 h, versus ∼70 h for Alpha-Sentry) for actinides of interest while also remaining ∼100% blind to ∼10 3 × higher Rn-progeny background—with the added potential for offering few keV scale energy resolution without resorting to peak shape fitting, versus ∼300–400 keV for existing CAM systems.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Pulse shape discrimination in CUPID-Mo using principal component analysis

CUPID-Mo is a cryogenic detector array designed to search for neutrinoless double-beta decay ($0\nu\beta\beta$) of $^{100}$Mo. It uses 20 scintillating $^{100}$Mo-enriched Li$_2$MoO$_4$ bolometers instrumented with Ge light detectors to perform active suppression of $\alpha$ backgrounds, drastically reducing the expected background in the $0\nu\beta\beta$ signal region. As a result, pileup events and small detector instabilities that mimic normal signals become non-negligible potential backgrounds. These types of events can in principle be eliminated based on their signal shapes, which are different from those of regular bolometric pulses. We show that a purely data-driven principal component analysis based approach is able to filter out these anomalous events, without the aid of detector response simulations.

47 OTHER INSTRUMENTATION↗