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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 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

Multi-Dimensional Spectral Difference Method for Unstructured Grids

A new, high-order, conservative, and efficient method for conservation laws on unstructured grids is developed. It combines the best features of structured and unstructured grid methods to attain computational efficiency and geometric flexibility; it utilizes the concept of discontinuous and high-order local representations to achieve conservation and high accuracy; and it is based on the finite-difference formulation for simplicity. Universal reconstructions are obtained by distributing unknowns in a geometrically similar manner for all unstructured cells. Placements of the unknown and flux points with various order of accuracy are given for the line, triangular and tetrahedral elements. The data structure of the new method permits an optimum use of cache memory, resulting in further computational efficiency on modern computers. A new pointer system is developed that reduces memory requirements and simplifies programming for any order of accuracy. Numerical solutions are presented and compared with the exact solutions for wave propagation problems in both two and three dimensions to demonstrate the capability of the method. Excellent agreement has been found. The method is simpler and more efficient than previous discontinuous Galerkin and spectral volume methods for unstructured grids.

Liu, Yen↗
NASA NTRS1992

Laboratory Reflectance Spectra of 160 Minerals, 0.4 to 2.5 Micrometers

This reports provides reflectance spectra of 160 minerals in both digital and printed form. In order to demonstrate the effect of particle size on reflectance, the spectral data for 135 of the minerals are presented at three different grain sizes. These are 125-500 microns, 45-125 microns and less than 45 microns. Ancillary information is provided with each mineral spectrum, which includes the mineral name, minerology, supplier, sampling locality and our designated sample number. The purity of every mineral sample was evaluated by X-ray diffraction (XRD). The composition of certain minerals known to deviate strongly from idealized end-member compositions was determined by electron microprobe analysis. The compositional information obtained by microbe analysis and accessory minerals identified by XRD are noted with the ancillary information. In addition, the spectrum acquired from the coarsest grain size available for each sample was processed with a feature-finding algorithm to quantify the characteristics of the spectral absorption features. All the reflectance spectra presented here are provided in digital form on IBM-compatible 3.5" diskettes. Also included on diskette is a program for displaying the spectral data and searching for spectral features that runs on an IBM-compatible PC with standard VCA graphics.

reflectance spectra↗
NASA NTRS1985

Active experiments from ground

Recent ground-based stimulation and observations of ionospheric and magnetospheric phenomena are reported. The studies included amplification and emission generation by coherent ducted whistler mode signals in the magnetosphere, recipitation of radiation belt particles by the injection of VLF waves from ground-based sources, spectral broadening of the VLF signals during ionospheric propagation and the generation of ELF/VLF signals by HF heating of the auroral electrojet. The capabilities of controlled stimulation of the local terrestrial magnetic field environment provides the means for further investigations into the processes of energy exchange between waves and radiation belt particles and the interrelationships of the exchange with the energy coupling between the magnetosphere and ionosphere.

Inan, U. S.↗
NASA NTRS1992

Upper tropospheric equatorial waves in ECMWF analyses

An observational study is presented of travelling waves in the near-equatorial upper tropospheric wind field as revealed in operational analyses produced by the European Center for Medium-range Weather Forecasts (ECMWF) over the years 1980-1987. Space-time spectra are presented that reveal the seasonal and interannual variability of traveling waves in the tropical wind fields. The zonal wind spectra exhibit a majority of power in the lowest resolved frequencies, and there is a lack of notable spectral peaks. The upper tropospheric meridional wind spectra show maxima for westward-propagating zonal waves 4-7 with 6- to 10-day periods. The events are also longitudinally localized, with a preference for westward-propagating waves occurring over the eastern Pacific Ocean during August-September. The waves exhibit maximum amplitudes in the upper troposphere and weak coherence with the near-surface layers of the atmosphere.

Randel, William J.↗
NASA NTRS1954

Characteristics of turbulence in a boundary layer with zero pressure gradient

The results of an experimental investigation of a turbulent boundary layer with zero pressure gradient are presented. Measurements with the hot-wire anemometer were made of turbulent energy and turbulent shear stress, probability density and flattening factor of u-fluctuation, spectra of turbulent energy and shear stress, and turbulent dissipation. The importance of the region near the wall and the inadequacy of the concept of local isotropy are demonstrated. Attention is given to the energy balance and the intermittent character of the outer region of the boundary layer. Also several interesting features of the spectral distribution of the turbulent motions are discussed.

FLOW, TURBULENT↗
NASA NTRS1955

Characteristics of turbulence in boundary layer with zero pressure gradient

The results of an experimental investigation of a turbulent boundary layer with zero pressure gradient are presented. Measurements with the hot-wire anemometer were made of turbulent energy and turbulent shear stress, probability density and flattening factor of u-fluctuation (fluctuation in x-direction), spectra of turbulent energy and shear stress, and turbulent dissipation. The importance of the region near the wall and the inadequacy of the concept of local isotropy are demonstrated. Attention is given to the energy balance and the intermittent character of the outer region of the boundary layer. Also several interesting features of the spectral distribution of the turbulent motions are discussed.

Klebanoff, P S↗
NASA NTRS1992

On the local nature of the energy cascade

The local nature of the energy cascade in space and time is studied using direct numerical simulation of decaying and forced isotropic turbulence. To examine the concept that large scales evolve into smaller ones, we compute the Lagrangian correlation coefficient between local kinetic energy at different scales. This correlation is found to peak at a Lagrangian time-delay that increases with scale separation. The results show that, on average, the flow of energy to smaller scales is predominantly local in physical space and that the view of eddies decaying into smaller ones while transferring their kinetic energy appears to be, on average, quite realistic. To examine the spectral characteristics of the cascade under unsteady conditions, a pulse of large-scale energy is added to the large-eddy simulation of forced isotropic turbulence. As time progresses, the evolution of this pulse through bands of increasing wavenumbers is studied.

Meneveau, C.↗
NASA NTRS1995

Field lines and magnetic surfaces in a two-component slab/2D model of interplanetary magnetic fluctuations

A two-component model for the spectrum of interplanetary magnetic fluctuations was proposed on the basis of ISEE observations, and has found an intriguing level of application in other solar wind studies. The model fluctuations consist of a fraction of 'slab' fluctuations, varying only in the direction parallel to the locally uniform mean magnetic field B(0) and a complement of 2D (two-dimensional) fluctuations that vary in the directions transverse to B(0). We have developed an spectral method computational algorithm for computing the magnetic flux surfaces (flux tubes) associated with the composite model, based upon a precise analogy with equations for ideal transport of a passive scalar in planar two dimensional geometry. Visualization of various composite models will be presented, including the 80 percent 2D/ 20 percent slab model with delta B/B(0) approximately equals 1 and a minus 5/3 spectral law, that is thought to approximately represent a snapshot of solar wind turbulence. Characteristically, the visualizations show that flux tubes, even when defined as regular on some plane, shred and disperse rapidly as they are viewed along the parallel direction. This diffusive process, which generalizes the standard picture of field line random walk, will be discussed in detail. Evidently, the traditional picture that flux tubes randomize like strands of spaghetti with a uniform tangle along the axial direction is in need of modification.

Matthaeus, W. H.↗
NASA NTRS2010

High Performance Non-Dispersive X-Ray Spectrometers for Charge Exchange Measurements

Currently, the only measurements of cosmological charge exchange have been made using low resolution, non-dispersive spectrometers like the PSPC on ROSAT and the CCD instruments on Chandra and XMM/Newton. However, upcoming cryogenic spectrometers on Astro-H and IXO will add vast new capabilities to investigate charge exchange in local objects such as comets and planetary atmospheres. They may also allow us to observe charge exchange in extra-solar objects such as galactic supernova remnants. With low spectral resolution instruments such as CCDs, x-ray emission due to charge exchange recombination really only provides information on the acceptor species, such as the solar wind. With the new breed of x-ray calorimeter instruments, emission from charge exchange becomes highly diagnostic allowing one to uniquely determine the acceptor species, ionization state, donor species and ionization state, and the relative velocity of the interaction. We will describe x-ray calorimeter instrumentation and its potential for charge exchange measurements in the near term. We will also touch on the instrumentation behind a decade of high resolution measurements of charge exchange using an x-ray calorimeter at the Lawrence Livermore National Laboratory.

Porter Frederick↗
NASA NTRSDate not supplied

Stability Analysis of the Flow over a Swept Forward-Facing Step using PIV Base Flowsin a Non-Orthogonal Coordinate System

Understanding the flow of a crossflow-vortex-dominated boundary layer over a forward-facing step excrescence is necessary in order to mitigate an early transition scenario on the wings and tail of commercial aircraft. By performing BiGlobal stability analysis on the flowfield measured with high-resolution, stereographic Particle Image Velocimetry (PIV), previous work has shown that a family of unstable disturbances exists in the direct downstream vicinity of a supercritical, forward-facing step. The goal of the present paper is to improve the previously used stability approach on two fronts: 1) the stability problem is formulated in a non-orthogonal coordinate system and 2) the contribution of the out-of-plane base-flow derivatives is accounted for locally. The resulting eigen solutions feature significantly stronger growth rates and eigenfunctions that are localized above regions of reverse flow. The changes in the problem formulation furthermore establish a significant improvement in the comparison of the stability solutions with the results from the Spectral Proper Orthogonal Decomposition (SPOD) of a time-resolved measurement of the perturbation content. A large destabilizing effect by the out-of-plane base-flow derivatives is determined to be justified, despite the assumption that these derivatives are small, because the effect can be reconstructed upon using an eigenvalue-correction formula that assumes the responsible terms are infinitesimally small. The unstable perturbation mechanisms are demonstrated to have a convective nature by assessing the relation between the frequency and the out-of-plane wavenumber, which indicates that their group speed does not approach zero. The last 2 facts, that 1) the perturbations are convective and 2) that the out-of-plane base-flow-derivative terms are small, remove any qualitative suspicions that the perturbation problem is not conducive to parabolization. This opens the path to analyzing this problem with a plane-marching approach.

Boundary- Layer Transition↗
NASA NTRS1990

Classification of auroral precipitation fluxes by characteristic parameters and their effects on the coupling of the precipitation to the ambient ionosphere

The spectral shapes of the precipitating auroral electron flux spectra are quantified by an automated fitting procedure which represents each flux spectrum as a superposition of Maxwellian and Gaussian partial fluxes. This makes it possible to represent each spectrum by a set of characteristic parameters which describe the shape of that spectrum. A set of inverted-V events observed by the Low-Energy Plasma Instrument on Dynamics Explorer 2 near the fall 1981 equinox, has been analyzed. The distribution of the peak inverted-V energies in magnetic local time and invariant latitude (IL) has been obtained, and it is shown that by far the highest peak energies occur in the range of IL between 65 and 70 and MLT between 18 and 24 hrs. It is also shown how the difference in spectral characteristics of the precipitation fluxes between the cusp and the nighttime auroral zone determines the thermal coupling of the precipitation to the ambient ionosphere.

Fontheim, E. G.↗
NASA NTRS1976

Image quality prediction - An aid to the Viking lander imaging investigation on Mars

Image quality criteria and image quality predictions are formulated for the multispectral panoramic cameras carried by the Viking Mars landers. Image quality predictions are based on expected camera performance, Mars surface radiance, and lighting and viewing geometry (fields of view, Mars lander shadows, solar day-night alternation), and are needed in diagnosis of camera performance, in arriving at a preflight imaging strategy, and revision of that strategy should the need arise. Landing considerations, camera control instructions, camera control logic, aspects of the imaging process (spectral response, spatial response, sensitivity), and likely problems are discussed. Major concerns include: degradation of camera response by isotope radiation, uncertainties in lighting and viewing geometry and in landing site local topography, contamination of camera window by dust abrasion, and initial errors in assigning camera dynamic ranges (gains and offsets).

Huck, F. O.↗
NASA NTRS1977

Ozone monitoring with an infrared heterodyne radiometer

Measurements of the total burden and of the concentration-versus-altitude profiles of ozone have been made with a ground-based heterodyne radiometer at Pasadena, California. The measurements were made in the 9.5-micron wavelength region, where a strong ozone infrared absorption band exists. The radiometer measured solar absorption at selected wavelengths with a spectral resolution of 0.001 reciprocal centimeter, equivalent to the half-width of an ozone absorption line at the 10-millibar altitude level. A carbon dioxide laser served as the local oscillator. This technique can be used to gather important data on both tropospheric and stratospheric ozone, which are not readily accessible with other remote-sensing techniques.

Menzies, R. T.↗
NASA NTRS1985

The new solar magnetograph for the Canary Islands Observatory THEMIS

THEMIS was designed for accurate polarization measurements in order to determine the intensity and direction of the magnetic field without interference with the local variations of the thermodynamical parameters. That goal leads to the following requirements: (1) high spatial resolution in horizontal direction; (2) sufficient resolution in height, which requires observations in several spectral lines with a sufficient spectral resolution; (3) accurate polarization measurements; (4) adequate time coverage to follow the evolution of individual structures; (5) precise tracking and scanning mechanisms; and (6) sufficient field of view for the different observed structures. The design of the instrument is discussed in detail.

Rayrole, J.↗
NASA NTRS2001

HST/STIS Spectroscopy of the Local Lyman-Alpha Forest

The Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope has brought a new era in studying the low-redshift Lyman-alpha Forest. The advantages of STIS over previous HST spectrographs include:(l) a high spectral resolution (7 km/s) comparable to Keck/HIRES spectra of the high-redshift Lyman-alpha forest; (2) a high observing efficiency brought about by an imaging detector able to span the full fares wavelength range (1150-1700 A, or equivalently, z=0.0-0.4) in a single exposure. The STIS Investigation Definition Team is therefore conducting an observational program to determine the properties of the low-redshift intergalactic medium as manifested by the Lyman-alpha forest. The team has made observations of the quasars: 3C 273, 3C 351, and PKS 0405. We shall present results based on the sightline to 3C 273, the brightest of these sources.

Heap, Sara R.↗
NASA NTRS2012

Search for Olivine Spectral Signatures on the Surface of Vesta

The occurrence of olivines on Vesta were first postulated from traditional petrogenetic models which suggest the formation of olivine as lower crustal cumulates. An indirect confirmation is given by their presence as a minor component in some samples of diogenite meteorites, the harzburgitic diogenites and the dunitic diogenites, and as olivine mineral clasts in howardites. Another indication for this mineral was given by interpretations of groundbased and Hubble Space Telescope observations that suggested the presence of local olivine-bearing units on the surface of Vesta. The VIR instrument onboard the DAWN mission has been mapping Vesta since July 2011. VIR acquired hyperspectral images of Vesta s surface in the wavelength range from 0.25 to 5.1 m during Approach, Survey and High Altitude Mapping (HAMO) orbits that allowed a 2/3 of the entire asteroid surface to be mapped. The VIR operative spectral interval, resolution and coverage is suitable for the detection and mapping of any olivine rich regions that may occur on the Vesta surface. The abundance of olivine in diogenites is typically lower than 10% but some samples richer in olivine are known. However, we do not expect to have extensive exposures of olivine-rich material on Vesta. Moreover, the partial overlap of olivine and pyroxene spectral signatures will make olivine difficult to detect. Different spectral parameters have been used to map olivine on extraterrestrial bodies, and here we discuss the different approaches used, and develop new ones specifically for Vesta. Our new methods are based on combinations of the spectral parameters relative to the 1 and 2 micron bands (the most prominent spectral features of Vesta surface in the visible and the infrared), such as band center locations, band depths, band areas, band area ratios. Before the direct application to the VIR data, the efficiency of each approach is evaluated by means of analysis of laboratory spectra of HED meteorites, pyroxenes, olivines and their mixtures.

Palomba, E.↗
NASA NTRS1999

CUSP Energetic Particles: Confinement, Acceleration and Implications

The cusp energetic particle (CEP) event is a new magnetospheric phenomenon. The events were detected in the dayside cusp for hours, in which the measured helium ions had energies up to 8 MeV. All of these events were associated with a dramatic decrease and large fluctuations in the local magnetic field strength. During January 1999 - December 1999 covered by this report, I have studied the CEP events by analyzing the POLAR, GEOTAIL, and WIND particle and magnetic field data measured during the geomagnetic quiet periods in 1996 and one geomagnetic storm period in 1998. The simultaneous observations indicated that the ion fluxes in the CEP events were higher than that in both the upstream and the downstream from the bow shock. The pitch angle distribution of the helium ions in the CEP events was found to peak around 90 deg. It was found that the mirror parameter, defined as the ratio of the square root of the integration of the parallel turbulent power spectral component over the ultra-low frequency (ULF) ranges to the mean field in the cusp, is correlated with the intensity of the cusp MeV helium flux, which is a measure of the influence of mirroring interactions and an indication of local effect. It was also found that the turbulent power of the local magnetic field in the ultra-low frequency (ULF) ranges is correlated with the intensity of the cusp energetic helium ions. Such ULF ranges correspond to periods of about 0.33-500 seconds that cover the gyroperiods, the bounce periods, and the drift periods of the tens keV to MeV charged particles when they are temporarily confined in the high-altitude dayside cusp. These observations represent a discovery that the high-altitude dayside cusp is a new acceleration and dynamic trapping region of the magnetosphere. The cusp geometry is connected via gradient and curvature drift of these energized ions to the equatorial plasma sheet as close as the geostationary orbit at local midnight. It implies that the dayside cusp is potentially an important source of magnetospheric particles. The discovery of the CEP events has been recognized as one of the most significant results from POLAR. I was invited to give a talk at 1999 IUGG meeting to interpret the CEP events. This discovery has also been written into the web-based Space Physics Text Book (http://www.oulu.fi/- spaceweb/textbook/cusp.html).

Chen, Jiasheng↗
NASA NTRS1993

Measurement methods and algorithms for comparison of local and remote clocks

Several methods for characterizing the performance of clocks with special emphasis on using calibration information that is acquired via an unreliable or noisy channel is discussed. Time-domain variance estimators and frequency-domain techniques such as cross-spectral analysis are discussed. Each of these methods has advantages and limitations that will be illustrated using data obtained via GPS, ACTS, and other methods. No one technique will be optimum for all of these analyses, and some of these problems cannot be completely characterized by any of the techniques discussed. The inverse problem of communicating frequency and time corrections to a real-time steered clock are also discussed. Methods were developed to mitigate the disastrous problems of data corruption and loss of computer control.

Levine, Judah↗