Temperature and composition of the equatorial ionosphere.
Equatorial ionosphere charged particle composition and ion and electron temperatures using incoherent scattering autocorrelation function
Farley, D. T.↗
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Stardust Interstellar Preliminary Examination IX: High-Speed Interstellar Dust Analog Capture in Stardust Flight-Spare Aerogel
The NASA Stardust mission used silica aerogel slabs to slowly decelerate and capture impinging cosmic dust particles for return to Earth. During this process, impact tracks are generated along the trajectory of the particle into the aerogel. It is believed that the morphology and dimensions of these tracks, together with the state of captured grains at track termini, may be linked to the size, velocity, and density of the impacting cosmic dust grain. Here, we present the results of laboratory hypervelocity impact experiments, during which cosmic dust analog particles (diameters of between 0.2 and 0.4 lm), composed of olivine, orthopyroxene, or an organic polymer, were accelerated onto Stardust flight spare low-density (approximately 0.01 g/cu cm) silica aerogel. The impact velocities (3-21 km/s) were chosen to simulate the range of velocities expected during Stardust's interstellar dust (ISD) collection phases. Track lengths and widths, together with the success of particle capture, are analyzed as functions of impact velocity and particle composition, density, and size. Captured terminal particles from low-density organic projectiles become undetectable at lower velocities than those from similarly sized, denser mineral particles, which are still detectable (although substantially altered by the impact process) at 15 km/s. The survival of these terminal particles, together with the track dimensions obtained during low impact speed capture of small grains in the laboratory, indicates that two of the three best Stardust candidate extraterrestrial grains were actually captured at speeds much lower than predicted. Track length and diameters are, in general, more sensitive to impact velocities than previously expected, which makes tracks of particles with diameters of 0.4 lm and below hard to identify at low capture speeds (<10 km/s). Therefore, although captured intact, the majority of the interstellar dust grains returned to Earth by Stardust remain to be found.
Stardust↗
SiLix-C Nanocomposites
For this Phase II project, Superior Graphite Co., in collaboration with the Georgia Institute of Technology and Streamline Nanotechnologies, Inc., developed, explored the properties of, and demonstrated the enhanced capabilities of novel nanostructured SiLix-C anodes. These anodes can retain high capacity at a rapid 2-hour discharge rate and at 0 C when used in Li-ion batteries. In Phase I, these advanced anode materials had specific capacity in excess of 1,000 mAh/g, minimal irreversible capacity losses, and stable performance for 20 cycles at C/1. The goals in Phase II were to develop and apply a variety of novel nanomaterials, fine-tune the properties of composite particles at the nanoscale, optimize the composition of the anodes, and select appropriate binder and electrolytes. In order to achieve a breakthrough in power characteristics of Li-ion batteries, the team developed new nanostructured SiLix-C anode materials to offer up to 1,200 mAh/g at C/2 at 0 C.
Henry, Francois↗
Particle Shape and Composition of NU-LHT-2M
Particle shapes of the lunar regolith simulant NU-LHT-2M were analyzed by scanning electron microscope of polished sections. These data provide shape, size, and composition information on a particle by particle basis. 5,193 particles were measured, divided into four sized fractions: less than 200 mesh, 200-100 mesh, 100-35 mesh, and greater than 35 mesh. 99.2% of all particles were monominerallic. Minor size versus composition effects were noted in minor and trace mineralogy. The two metrics used are aspect ratio and Heywood factor, plotted as normalized frequency distributions. Shape versus composition effects were noted for glass and possibly chlorite. To aid in analysis, the measured shape distributions are compared to data for ellipses and rectangles. Several other simple geometric shapes are also investigated as to how they plot in aspect ratio versus Heywood factor space. The bulk of the data previously reported, which were acquired in a plane of projection, are between the ellipse and rectangle lines. In contrast, these data, which were acquired in a plane of section, clearly show that a significant number of particles have concave hulls in this view. Appendices cover details of measurement error, use of geometric shapes for comparative analysis, and a logic for comparing data from plane of projection and plane of section measurements.
Rickman, D. L.↗
Dust in the Mars atmosphere
The amount of dust suspended in the Martian atmosphere is highly variable with location and with time. The opacity of the sky is best known at the two Viking Lander sites, where visual, vertical-column optical depth never fell below a value of a few tenths during the 1.25 Mars years of observations and yet exceeded 2 to 3 during two great dust storms in 1977. Elsewhere on the planet, optical depths have been estimated from orbiter visible imaging of surface contrasts and from mapping of infrared emission from the surface and the overlying (dusty) atmosphere. In many cases these opacities (and thus dust amounts) may be uncertain by as much as a factor of two. Viking Lander observations of twilight indicate that the background dust haze is more or less uniformly mixed with altitude in the lower atmosphere. Observations from spacecraft indicate that there may be come seasonal variations to the height of these dust hazes, which sometimes extend above 30 km. (Ice haze layers may occur as high as 80 km.) The existing observations do not constrain the composition or the size distribution of the suspended dust particles very well. Remote sensing observations depend principally upon the product of the number of particles, the geometric cross-sections (and so particle size and shape), and the extinction efficiency of the particles (and so the particle composition), as integrated over the particle size distribution and along the line of sight. While the observed variation of dust opacity with wavelength constrains these quantities, it does not often permit the unique determination of the individual properties of the suspended dust. A size distribution having a cross-section weighted mean particle radius of 2.5 microns was deduced from a synthesis of the IR thermal emission spectra observed in the Southern Hemisphere by Mariner 9 during the 1971 global dust storm. Although the IR thermal emission is relatively insensitive to the sub-micron sized particles which tend to dominate visible opacity, this same size distribution was consistent with modeling of the sky brightness variation near the sun, as seen through the background haze above the Viking lander sites in the Northern Hemisphere.
Zurek, R. W.↗
Fine Aerosol Bulk Composition Measured on WP-3D Research Aircraft in Vicinity of the Northeastern United States - Results from NEAQS
During the New England Air Quality Study (NEAQS) in the summer of 2004, airborne measurements were made of the major inorganic ions and the water-soluble organic carbon (WSOC) of the submicron (PM(sub 1.0)) aerosol. These and ancillary data are used to describe the overall aerosol chemical characteristics encountered during the study. Fine particle mass was estimated from particle volume and a calculated density based on measured particle composition. Fine particle organic matter (OM) was estimated from WSOC and a mass balance analysis. The aerosol over the northeastern United States (U.S.) and Canada was predominantly sulfate and associated ammonium, and organic components, although in unique plumes additional ionic components were also periodically above detection limits. In power generation regions, and especially in the Ohio River Valley region, the aerosol tended to be predominantly sulfate (approximately 60% micro gram /micro gram) and apparently acidic, based on an excess of measured anions compared to cations. In all other regions where sulfate concentrations were lower and a smaller fraction of overall mass, the cations and anions were balanced suggesting a more neutral aerosol. In contrast, the WSOC and estimated OM were more spatially uniform and the fraction of OM relative to PM mass was largely influenced by sources of sulfate. The study median OM mass fraction was 40%. Throughout the study region, sulfate and organic aerosol mass were highest near the surface and decreased rapidly with increasing altitude. The relative fraction of organic mass to sulfate was similar throughout all altitudes within the boundary layer (altitude less than 2.5 km), but was significantly higher at altitude layers in the free troposphere (above 2.5 km). A number of distinct biomass burning plumes from fires in Alaska and the Yukon were periodically intercepted, mostly at altitudes between 3 and 4 km. These plumes were associated with highest aerosol concentrations of the study and were largely comprised of organic aerosol components (approximtely 60%).
Peltier, R. E.↗
Diagnostics of wear in aeronautical systems
Maintenance costs associated with the transmissions and drive train greatly increase the maintenance burden and failure risk. Detection measurements fall under two general categories of vibration and particle detectors. The latter are more amenable to tracking wear. Wear debris analysis can supply a great deal of information such as: particle concentration, rate of change in concentration, composition, particle size and shape, principal metals, etc. It is not economically feasible to monitor all variables. At least one role of the lubrication and wear specialist is to provide guidance in selecting the most appropriate variables to monitor.
Wedeven, L. D.↗
Boundary Layer Aerosol Composition over Sierra Nevada Mountains using 9.11- and 10.59-micron CW Lidars and Modeled Backscatter from Size Distribution Data
An inversion technique has been developed to determine volume fractions of an atmospheric aerosol composed primarily of ammonium sulfate and ammonium nitrate and water combined with fixed concentration of elemental and organic carbon. It is based on measured aerosol backscatter obtained with 9.11 - and 10.59-micron wavelength continuous wave CO2 lidars and modeled backscatter from aerosol size distribution data. The technique is demonstrated during a flight of the NASA DC-8 aircraft over the Sierra Nevada Mountain Range, California on 19 September, 1995. Volume fraction of each component and effective complex refractive index of the composite particle were determined assuming an internally mixed composite aerosol model. The volume fractions were also used to re-compute aerosol backscatter, providing good agreement with the lidar-measured data. The robustness of the technique for determining volume fractions was extended with a comparison of calculated 2.1,-micron backscatter from size distribution data with the measured lidar data converted to 2.1,-micron backscatter using an earlier derived algorithm, verifying the algorithm as well as the backscatter calculations.
Cutten, D. R.↗
Aerosol–Ice Formation Closure: A Southern Great Plains Field Campaign
Prediction of ice formation in clouds presents one of the grand challenges in the atmospheric sciences. Immersion freezing initiated by ice-nucleating particles (INPs) is the dominant pathway of primary ice crystal formation in mixed-phase clouds, where supercooled water droplets and ice crystals coexist, with important implications for the hydrological cycle and climate. However, derivation of INP number concentrations from an ambient aerosol population in cloud-resolving and climate models remains highly uncertain. We conducted an aerosol-ice formation closure pilot study using a field-observational approach to evaluate the predictive capability of immersion freezing INPs. The closure study relies on co-located measurements of the ambient size-resolved and single-particle composition and INP number concentrations. The acquired particle data serve as input in several immersion freezing parameterizations, that are employed in cloud-resolving and climate models, for prediction of INP number concentrations. We discuss in detail one closure case study in which a front passed through the measurement site, resulting in a change of ambient particle and INP populations. We achieved closure in some circumstances within uncertainties, but we emphasize the need for freezing parameterization of potentially missing INP types and evaluation of the choice of parameterization to be employed. Overall, this closure pilot study aims to assess the level of parameter details and measurement strategies needed to achieve aerosol-ice formation closure. The closure approach is designed to accurately guide immersion freezing schemes in models, and ultimately identify the leading causes for climate model bias in INP predictions.
ice formation↗
Composition of energetic particles from solar flares
We present a model for composition of heavy ions in the Solar Energetic Particles (SEP). The SEP composition in a typical large solar particle event reflects the composition of the Sun, with adjustments due to fractionation effects which depend on the First Ionization Potential (FIP) of the ion and on the ratio of ionic charge to mass (Q/M). Flare-to flare variations in composition are represented by parameters describing these fractionation effects and the distributions of these parameters are presented.
Garrard, T. L.↗
Preparation of composite materials in space. Volume 1: Executive summary
The reported objectives were to define promising materials, to obtain significant processing criteria and the related processing techniques and apparatus for the preparation of composites in space, and to establish a program for zero-g experiments and the required developmental efforts. Preparation was studied of the following composite types: (1) metal-base fiber and particle composites, including cemented compacts, (2) controlled density metals, comprising plain and reinforced metal foams, and (3) unidirectionally solidified eutectic alloys. The zero-g environment of orbital operations offers the capability to produce metal-base composite materials and castings which exhibit properties and, particularly, unique combinations of properties that cannot be achieved in terrestrial production.
Steurer, W. H.↗
Sounding rocket measurements of ion composition and charged particle temperatures in the topside ionosphere.
Ion composition and charged particle temperatures at 300-600 km from sounding rocket and topside sounder Alouette 2 measurements
Maier, E. J. R.↗
Symmetry considerations in the scattering of identical composite bodies
Previous studies of the interactions between composite particles were extended to the case in which the composites are identical. The form of the total interaction potential matrix elements was obtained, and guidelines for their explicit evaluation were given. For the case of elastic scattering of identical composites, the matrix element approach was shown to be equivalent to the scattering amplitude method.
Norbury, J. W.↗
Suggestion for extended Viking magnetic properties experiment on future Mars missions
A remarkable result from the Viking missions was the discovery that the Martian soil is highly magnetic, in the sense that the soil is attracted by a small magnet. The soil was found to adhere almost equally well to a strong and a weak SmCo magnet in the Viking lander backhoe at both landing sites. An array of permanent magnets, with the purpose of establishing if the magnetic particles on Mars are present as discrete or as composite particles, has been constructed.
Madsen, M. B.↗
Uncertainties in the Thermal and Mechanical Properties of Particulate Composites Quantified
Particle-reinforced composites are candidate materials for a wide variety of aerospace and nonaerospace applications. The high costs and technical difficulties involved with the use of many fiber-reinforced composites often limit their use in many applications. Consequently, particulate composites have emerged as viable alternatives to conventional fiber-reinforced composites. Particulate composites can be processed to near net shapepotentially reducing the manufacturing costs. They are candidate materials where shock or impact properties are important. For example, particle-reinforced metal matrix composites have shown great potential for many automotive applications. Typically, these materials are aluminum matrix reinforced with SiC or TiC particles. Reinforced concrete can also be thought of as a particle-reinforced composite. In situ ceramics can be modeled as particulate composites and are candidate materials for many high-temperature applications. The characterization of these materials is fundamental to their reliable use. It has been observed that the overall properties of these composites exhibit scatter because of the uncertainty in the constituent material properties, and fabrication-related parameters.
Murthy, Pappu L. N.↗
Space processing of composite materials
Materials and processes for the testing of aluminum-base fiber and particle composites, and of metal foams under extended-time low-g conditions were investigated. A wetting and dispersion technique was developed, based on the theory that under the absence of a gas phase all solids are wetted by liquids. The process is characterized by a high vacuum environment and a high temperature cycle. Successful wetting and dispersion experiments were carried out with sapphire fibers, whiskers and particles, and with fibers of silicon carbide, pyrolytic graphite and tungsten. The developed process and facilities permit the preparation of a precomposite which serves as sample material for flight experiments. Low-g processing consists then merely in the uniform redistribution of the reinforcements during a melting cycle. For the preparation of metal foams, gas generation by means of a thermally decomposing compound was found most adaptable to flight experiments. For flight experiments, the use of compacted mixture of the component materials limits low-g processing to a simple melt cycle.
Steurer, W. H.↗
Energy dependence in solar cosmic ray composition
An investigation is conducted concerning an occurrence of effects related to energy dependence in studies of solar flare particle composition, taking into account eight large solar-flares associated particle events. The ratios C/O (carbon/oxygen), (MG plus Si)/O, and Fe(group)/O as a function of energy/nucleon are presented in a graph. A wide range of variation in the Fe(group)/O ratios is found from event to event. While the energy dependence is consistent in most events with individual element spectra, several events show unusual behavior in the Fe(group)/O ratio, due to the existence of several distinct spectral components. These multiple spectral components may imply multiple phases of acceleration or substantial interplanetary shock contamination at low energies at times well below the arrival time of these shocks at 1 AU.
Mcguire, R. E.↗
Preparation of composite materials in space. Volume 2: Technical report
A study to define promising materials, significant processing criteria, and the related processing techniques and apparatus for the preparation of composite materials in space was conducted. The study also established a program for zero gravity experiments and the required developmental efforts. The following composite types were considered: (1) metal-base fiber and particle composites, including cemented compacts, (2) controlled density metals, comprising plain and reinforced metal foams, and (3) unidirectionally solidified eutectic alloys. A program of suborbital and orbital experiments for the 1972 to 1978 time period was established to identify materials, processes, and required experiment equipment.
Steurer, W. H.↗