Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “particle data”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,783 records · Page 99
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

The 27-28 October 1986 FIRE IFO cirrus case study: Comparison of satellite and aircraft derived particle size

Theoretical calculations predict that cloud reflectance in near infrared windows such as those at 1.6 and 2.2 microns should give lower reflectances than at visible wavelengths. The reason for this difference is that ice and liquid water show significant absorption at those wavelengths, in contrast to the nearly conservative scattering at wavelengths shorter than 1 micron. In addition, because the amount of absorption scales with the path length of radiation through the particle, increasing cloud particle size should lead to decreasing reflectances at 1.6 and 2.2 microns. Measurements at these wavelengths to date, however, have often given unpredicted results. Twomey and Cocks found unexpectedly high absorption (factors of 3 to 5) in optically thick liquid water clouds. Curran and Wu found expectedly low absorption in optically thick high clouds, and postulated the existence of supercooled small water droplets in place of the expected large ice particles. The implications of the FIRE data for optically thin cirrus are examined.

Wielicki, Bruce A.↗
NASA NTRS1991

Origins of magnetospheric plasma

A review is given of recent (1987-1990) progress in understanding of the origins of plasmas in the earth's magnetosphere. In counterpoint to the early supposition that geomagnetic phenomena are produced by energetic plasmas of solar origin, 1987 saw the publication of a provocative argument that accelerated ionospheric plasma could supply all magnetospheric auroral and ring current particles. Significant new developments of existing data sets, as well as the establishment of entirely new data sets, have improved the ability to identify plasma source regions and to track plasma through the magnetospheric system of boundary layers and reservoirs. These developments suggest that the boundary between ionospheric and solar plasmas, once taken to lie at the plasmapause, actually lies much nearer to the magnetopause. Defining this boundary as the surface where solar wind and ionosphere contribute equally to the plasma, it is referred to herein as the 'geopause'. It is now well established that the infusion of ionospheric O(+) plays a major role in the storm-time distention of the magnetotail and inflation of the inner magnetosphere. After more than two decades of observation and debate, the question remains whether magnetosheric are protons of solar or terrestrial origin.

Moore, Thomas E.↗
NASA NTRS1991

Multifrequency radio observations of Saturn at ring inclination angles between 5 and 26 degrees

In order to investigate hypothesized latitudinal variations in the thermal emission from Saturn, the planet has been imaged at different wavelengths by the VLA and BIMA arrays. A bright band is found at 6 and 20 cm at midnorthern latitudes. The latitudinal brightness variation is suggested to be due to variations in the location of the NH4SH cloud. The extant data base on ring brightness temperatures and optical depths has been expanded by the present efforts. The data obtained are congruent with ice particles of the order of millimeters-meters in size; the number of particles has a power-law distribution that is proportionate to the radius cubed.

De Pater, Imke↗
NASA NTRS1990

Cosmic rays in the heliosphere - Present status and future opportunities

The general theory of charged-particle transport and acceleration is reviewed and application to the heliosphere discussed in detail. The present status of understanding is briefly surveyed, with emphasis on large-scale processes. Opportunities for increasing understanding through the confrontation of theory, modeling and observations are outlined. It is concluded that the largest advances in this understanding in the next few years will come from coordinated theoretical and observations studies of large-scale phenomena requiring energetic-particle, magnetic-field, and plasma data from several spacecraft. Fundamental studies of the interactions between cosmic rays and turbulent plasma to study transport coefficients, details of interactions with shocks, etc, are also important in the longer term.

Jokipii, J. R.↗
NASA NTRS1993

Dynamics of the baryonic component in hierarchical clustering universes

I present self-consistent 3-D simulations of the formation of virialized systems containing both gas and dark matter in a flat universe. A fully Lagrangian code based on the Smoothed Particle Hydrodynamics technique and a tree data structure has been used to evolve regions of comoving radius 2-3 Mpc. Tidal effects are included by coarse-sampling the density of the outer regions up to a radius approx. 20 Mpc. Initial conditions are set at high redshift (z greater than 7) using a standard Cold Dark Matter perturbation spectrum and a baryon mass fraction of 10 percent (omega(sub b) = 0.1). Simulations in which the gas evolves either adiabatically or radiates energy at a rate determined locally by its cooling function were performed. This allows us to investigate with the same set of simulations the importance of radiative losses in the formation of galaxies and the equilibrium structure of virialized systems where cooling is very inefficient. In the absence of radiative losses, the simulations can be rescaled to the density and radius typical of galaxy clusters. A summary of the main results is presented.

Navarro, Julio↗
NASA NTRS1994

Highly transparent and rugged sensor for velocity determinations of cosmic dust particles

In order to understand the evolution of interplanetary dust, numerous dust particles have been collected and analyzed. An analysis of the composition often provides information on the particle's origin. So does its origin. Composition and orbit data complement each other and should be determined together. If the last orbit of a particle can be determined, its orbital history can often be calculated backward in time and associated with its parent body. To determine the last orbit, the velocity needs to be measured before the particle is collected. The precision required in determining the velocity components relative to the spacecraft should be 1 percent or better. A sensor for naturally charged cosmic dust particles is discussed. Two models of the sensor were tested, one with a free-falling steel ball and the other with particles accelerated to high speed. Analytic expressions of the sensor signals are presented and compared with the test results. The errors in speed and angle were estimated to be about 0.3 percent and 0.2 degrees respectively.

Auer, Siegfried↗
NASA NTRS1994

Stochastic acceleration of energetic ions in Jupiter's magnetosphere

An equation governing the combined radial diffusion and stochastic acceleration of super-Alfvenic ions by magnetohydrodynamic waves in Jupiter's outer magnetosphere is derived. The formulation is based upon a total energy invariant of the adiabatic transport which applies to an isotropic distribution undergoing rapid pitch angle scattering by waves. An analytic solution to the double diffusion equation is obtained and numerical results are presented for two models of ion injection. The first model assumes S(+) and O(+) are injected throughout a broad region of space through photoionization of Jupiter's magnetospheric neutral wind and obtain an initial energy corresponding to the local corotation energy after pickup by the planetary magnetic field. The second model assumes a monoenergetic distribution of energetic protons is implanted in the middle magnetosphere by the action of field-aligned potential drops in Jupiter's auroral ionosphere. For both light and heavy ions the injection process creates a seed population of particles which are further accelerated nonadiabatically by the MHD waves and adiabatically through radial diffusion. A comparison of the theoretical results with a recent data analysis of Voyager low-energy charged particle measurements is made with very good agreement, thus providing a rigorous quantitative account of and definitive explanation for the high-energy ion component of Jupiter's magnetosphere.

Barbosa, D. D.↗
NASA NTRS1995

Low-frequency fluctuations in the magnetosheath near the magnetopause

There are four low-frequency modes which may propagate in a high-beta nearly bi-Maxwellian plasma. These are the magnetosonic, Alfven, ion acoustic, and mirror modes. This manuscript defines a procedure based on linear Vlasov theory for the unique identification of these modes by use of transport ratios, dimensionless ratios of the fluctuating field and plasma quantities. A single parameter, the mode deviation is calculated using the plasma and magnetic field data gathered by the Active Magnetospheric Particle Tracer Explorers/Ion Release Module (AMPTE/IRM) spacecraft to identify the modes observed in the terrestial magnetosheath near the magnetopause. As well as determining the mode which best describes the observed fluctuations, it gives us a measure of whether or not the resulting identification is unique. Using 17 time periods temporally close to a magnetopause crossing, and confining our study to the frequency range from 0.01 to 0.04 Hz, we find that the only clearly identified mode in this frequency range is the mirror mode. Most commonly, the quasi-perpendicular mirror mode (with wave vector k roughly perpendicular to the background magnetic field B(sub zero) is observed. In two events the quasi-parallel mirror mode k parallel B(sub zero) was identified.

Denton, Richard E.↗
NASA NTRS1995

High angular resolution 30 microns observations of the Galactic Center

We have mapped the central 2 min (5 pc) of the Galaxy with 4 sec resolution at 30 microns, using the MSFC bolometer array on the NASA Infrared Telescope Facility at Mauna Kea. Complementary maps at 10 and 20 microns covering the same region were obtained contemporaneously with the same instrumentation. The maps encompass both the central cavity at the very center of the Galaxy and the disk of gas and dust which surrounds it. Our data show thermal emissions from dust particles within the cavity and - for the first time at this resolution - within the disk itself. The emission peaks at the position of IRS1 at all three wavelengths, and the 20/30 micron brightness ratio falls uniformly from this peak toward the outer regions of the source. The 30 micron emission correlates well with the HCN emission in the southwest portion of the circumnuclear disk and with the (O I) emission in the north. No feature is apparent at the position of SgrA at any of the three wavelengths. The circumnuclear disk was discovered from the KAO and has been extensively studied in both continuum and line emission in numerous subsequent flights. The poster will attempt to show how these latest ground-based observations intersect and build upon these airborne investigations.

Telesco, Charles M.↗
NASA NTRS1998

Electrodynamics of the Inner Magnetosphere Observed in the Dusk Sector by CRRES and DMSP during the Magnetic Storm of June 4-6, 1991

We compare equatorward/earthward boundaries of convection electric fields and auroral/plasma sheet electrons detected by the DMSP F8 and CRRES satellites during the June 1991 magnetic storm. Measurements come from the dusk magnetic local time sector where the ring current penetrates closest to the Earth. The storm was triggered by a rapid increase in the solar wind dynamic pressure accompanied by a southward turning of the interplanetary magnetic field (IMF). Satellite data show the following: (1) all particle and field boundaries moved equatorward/earthward during the initial phase, probably in response to the strong southward IMF turning; (2) electric field boundaries were either at lower magnetic L shells or close to the inner edge of ring current ions throughout the main and early recovery phases. Penetration earthward of the ring current occurred twice as the polar cap potential increased rapidly; (3) electric potentials at subauroral latitudes were large fractions of the total potentials in the afternoon cell, twice exceeding 60 kV; and (4) the boundaries of auroral electron precipitation were more variable than those of electric fields and mapped to lower L shells than where CRRES encountered plasma sheet electrons. Observations qualitatively agree with predictions of empirical models for auroral electron and electric field boundaries.

Bruke, W. J.↗
NASA NTRS2000

Fast Particle Methods for Multiscale Phenomena Simulations

We are developing particle methods oriented at improving computational modeling capabilities of multiscale physical phenomena in : (i) high Reynolds number unsteady vortical flows, (ii) particle laden and interfacial flows, (iii)molecular dynamics studies of nanoscale droplets and studies of the structure, functions, and evolution of the earliest living cell. The unifying computational approach involves particle methods implemented in parallel computer architectures. The inherent adaptivity, robustness and efficiency of particle methods makes them a multidisciplinary computational tool capable of bridging the gap of micro-scale and continuum flow simulations. Using efficient tree data structures, multipole expansion algorithms, and improved particle-grid interpolation, particle methods allow for simulations using millions of computational elements, making possible the resolution of a wide range of length and time scales of these important physical phenomena.The current challenges in these simulations are in : [i] the proper formulation of particle methods in the molecular and continuous level for the discretization of the governing equations [ii] the resolution of the wide range of time and length scales governing the phenomena under investigation. [iii] the minimization of numerical artifacts that may interfere with the physics of the systems under consideration. [iv] the parallelization of processes such as tree traversal and grid-particle interpolations We are conducting simulations using vortex methods, molecular dynamics and smooth particle hydrodynamics, exploiting their unifying concepts such as : the solution of the N-body problem in parallel computers, highly accurate particle-particle and grid-particle interpolations, parallel FFT's and the formulation of processes such as diffusion in the context of particle methods. This approach enables us to transcend among seemingly unrelated areas of research.

Koumoutsakos, P.↗
NASA NTRS1997

Direct Aerosol Radiative Forcing: Calculations and Measurements from the Tropospheric

Radiative forcing is defined as the change in the net (downwelling minus upwelling) radiative flux at a given level in the atmosphere. This net flux is the radiative power density available to drive climatic processes in the earth-atmosphere system below that level. Recent research shows that radiative forcing by aerosol particles is a major source of uncertainty in climate predictions. To reduce those uncertainties, TARFOX was designed to determine direct (cloud-free) radiative forcing by the aerosols in one of the world's major industrial pollution plumes--that flowing from the east coast of the US over the Atlantic Ocean. TARFOX measured a variety of aerosol radiative effects (including direct forcing) while simultaneously measuring the chemical, physical, and optical properties of the aerosol particles causing those effects. The resulting data sets permit a wide variety of tests of the consistency, or closure, among the measurements and the models that link them. Because climate predictions use the same or similar model components, closure tests help to assess and reduce prediction uncertainties. In this work we use the TARFOX-determined aerosol, gas, and surface properties to compute radiative forcing for a variety of aerosol episodes, with inadvisable optical depths ranging from 0.07 to 0.6. We calculate forcing by several techniques with varying degrees of sophistication, in part to test the range of applicability of simplified techniques--which are often the only ones feasible in climate predictions by general circulation models (GCMs). We then compare computed forcing to that determined from: (1) Upwelling and downwelling fluxes (0.3-0.7 mm and 0.7-3.0 mm) measured by radiometers on the UK MRF C-130. and (2) Daily average cloud-free absorbed solar and emitted thermal radiative flux at the top of the atmosphere derived from the AVHRR radiometer on the NOAA- 14 satellite. The calculations and measurements all yield aerosol direct radiative forcing in the range -50 to -190 W sq m per unit inadvisable optical depth. The magnitudes are about 15 to 100 times larger than the global-average direct forcing expected for the global-average sulfate aerosol optical depth of 0.04. The reasons for the larger forcing in TARFOX include the relatively large optical depths and the focus on cloud-free, daytime conditions over the dark ocean surface. These are the conditions that produce the actual major radiative forcing events that contribute to any global-average climate effect. Detailed comparisons of calculated and measured forcings for specific events are used for more refined tests of closure.

Russell, P. B.↗
NASA NTRS2003

A Test of Maxwell's Z Model Using Inverse Modeling

In modeling impact craters a small region of energy and momentum deposition, commonly called a "point source", is often assumed. This assumption implies that an impact is the same as an explosion at some depth below the surface. Maxwell's Z Model, an empirical point-source model derived from explosion cratering, has previously been compared with numerical impact craters with vertical incidence angles, leading to two main inferences. First, the flowfield center of the Z Model must be placed below the target surface in order to replicate numerical impact craters. Second, for vertical impacts, the flow-field center cannot be stationary if the value of Z is held constant; rather, the flow-field center migrates downward as the crater grows. The work presented here evaluates the utility of the Z Model for reproducing both vertical and oblique experimental impact data obtained at the NASA Ames Vertical Gun Range (AVGR). Specifically, ejection angle data obtained through Three-Dimensional Particle Image Velocimetry (3D PIV) are used to constrain the parameters of Maxwell's Z Model, including the value of Z and the depth and position of the flow-field center via inverse modeling.

Anderson, J. L. B.↗
NASA NTRS2003

Effect of gravitational sedimentation on simulated aerosol dispersion in the human acinus

We studied the effect of gravitational sedimentation on the dispersion of 0.5 and 1 micrometer-diameter particle boluses within a two-dimensional symmetric six-generation model of the human acinus. Boluses were introduced at the beginning of a 2-s inspiration immediately followed by a 4-s expiration, in normal gravity (1 G) and in the absence of gravity (0 G). The flow corresponded to a flow rate at the mouth of 500 ml/s. In 0 G, simulated dispersion (Hsim) was 16 ml for both particle sizes. In 1 G, Hsim was 71 and 242 ml for 0.5 and 1 micrometer-diameter particles, respectively, showing the effect of gravitational sedimentation. The difference between experimental data (J. Appl. Physiol. 86 (1999) 1402) and simulations was independent of particle size. This suggests that the residual dispersion was independent of the intrinsic properties of the particles and was more likely due to other mechanisms such as ventilation inhomogeneities, cardiogenic oscillations and alveolar wall motion. c2003 Elsevier Science Ltd. All rights reserved.

short duration↗
NASA NTRS2004

Simulation of Helium-3 Extraction from Lunar Ilmenite

Knowledge of the trapping mechanisms and diffusion characteristics of solar-wind implanted isotopes in the minerals of the lunar regolith will enable the optimization of the processes to extract solar wind gases from regolith particles. Extraction parameters include the temperature and duration of extraction, particle size, and gas yield. Diffusion data will increase the efficiency and profitability of future mining ventures. This data will also assist in optimizing the evaluations of various potential mining sites based on remote sensing data. For instance, if magnesian ilmenite (Mg,Fel.,Ti03) is found to retain He better than stoichiometric ilmenite (FeTi03), remote sensing data for Mg could be considered in addition to Ti and maturity data. The context of the currently discussed work is the mining of helium-3 for potential use as a fuel for fusion energy generation. However, the potential resources deposited by the solar wind include hydrogen (and derived water), helium-4, nitrogen and carbon. Implantation experiments such as those performed for helium isotopes in ilmenite are important for the optimized extraction of these additional resources. These experiments can easily be reproduced for most elements or isotopes of interest.

Kuhlman, K. R.↗
NASA NTRS2004

Meteoritical Astrophysics: A New Subdiscipline

A recent remarkable discovery by Katharina Lodders showed that the abundances of extinct radioactivities (relative to reference nuclei) in chondrites, achondrites, and irons are proportional to the squares of their mean lives, whereas no such abundance-mean life relationship is apparent for the data of calcium-aluminum rich inclusions (CAIs) and a variety of other inclusion types. In this talk I shall interpret these results in terms of galactic and solar nebula processes. The first step in organizing the data for interpretation is to require that both the abundance of the extinct radioactivity (as measured by its decay product abundance) and that of the reference nuclide should have the same nucleosynthesis history, or else that a correction to the ratio be made to compensate for the ratio of the two different production processes. The striking feature of this diagram is that the lower edge of the data (the Lodders Line) is remarkably straight; most of the data are derived from chondrites; and its slope on the log-log diagram is two. So the extinct radioactivities are present in proportion to the square of their mean lives. All the other data lie above the Lodders line in this diagram; the sources of that data are in general somewhat larger particles than those that have contributed to the Lodders Line. A straight relationship between abundances of extinct radioactivities

Cameron, A. G. W.↗
NASA NTRS2005

Experiment to Characterize Aircraft Volatile Aerosol and Trace-Species Emissions (EXCAVATE)

The Experiment to Characterize Aircraft Volatile and Trace Species Emissions (EXCAVATE) was conducted at Langley Research Center (LaRC) in January 2002 and focused upon assaying the production of aerosols and aerosol precursors by a modern commercial aircraft, the Langley B757, during ground-based operation. Remaining uncertainty in the postcombustion fate of jet fuel sulfur contaminants, the need for data to test new theories of particle formation and growth within engine exhaust plumes, and the need for observations to develop air quality models for predicting pollution levels in airport terminal areas were the primary factors motivating the experiment. NASA's Atmospheric Effects of Aviation Project (AEAP) and the Ultra Effect Engine Technology (UEET) Program sponsored the experiment which had the specific objectives of determining ion densities; the fraction of fuel S converted from S(IV) to S(VI); the concentration and speciation of volatile aerosols and black carbon; and gas-phase concentrations of long-chain hydrocarbon and PAH species, all as functions of engine power, fuel composition, and plume age.

Anderson, B. E.↗
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↗