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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

A Theory of the von Weimarn Rules Governing the Average Size of Crystals Precipitated from a Supersaturated Solution

More than 75 years ago, von Weimarn summarized his observations of the dependence of the average crystal size on the initial relative concentration supersaturation prevailing in a solution from which crystals were growing. Since then, his empirically derived rules have become part of the lore of crystal growth. The first of these rules asserts that the average crystal size measured at the end of a crystallization increases as the initial value of the relative supersaturation decreases. The second rule states that for a given crystallization time, the average crystal size passes through a maximum as a function of the initial relative supersaturation. Using a theory of nucleation and growth due to Buyevich and Mansurov, we calculate the average crystal size as a function of the initial relative supersaturation. We confirm the von Weimarn rules for the case where the nucleation rate is proportional to the third power or higher of the relative supersaturation.

Barlow, Douglas A.↗
NASA NTRS1994

Counting Condensation Nuclei in the Antarctic Ozone Mission

The work done on this grant primarily concerns the measurement of aerosol in the stratosphere from NASA ER-2 aircraft in studies of stratospheric ozone depletion in the northern and southern hemispheres. The ER-2 Condensation Nucleus Counter (CNC) measures the number concentration of particles in the diameter range of approximately 0.01 to 1 micron. The Passive Cavity Aerosol Spectrometer measures size distributions in the 0.17 to 3 micron diameter range. This instrument was upgraded during this grant period to a Focused Cavity Aerosol Spectrometer (FCAS). This upgrade permitted the instrument to measure particles as small as 0.05 micron in diameter. The inlet for the PCAS and FCAS was modified and characterized under this grant so that the modifications to the aerosol due to anisokinetic sampling and heating upon sampling and in transport to the measurement location were accounted for in the data analysis. These measurements permitted observations of particle production in the southern hemisphere winter polar vortex and observation of the impact of denitrification on the number concentration of the aerosol in the denitrified air. In the northern polar vortex, the measurements provided a characterization of the sulfate aerosol. Following the eruption of Mount Pinatubo in 1991, the measurements permitted an accurate characterization of the sulfate aerosol enhancements resulting from the eruption. This led to studies of the impact of heterogeneous chemistry on the partitioning of the partitioning of the reactive nitrogen species and the partitioning of the chlorine reservoir.

Wilson, James Charles↗
NASA NTRS1993

Cratering in glasses impacted by debris or micrometeorites

Mechanical strength measurements on five glasses and one glass-ceramic exposed on LDEF revealed no damage exceeding experimental limits of error. The measurement technique subjected less than 5 percent of the sample surface area to stresses above 90 percent of the failure strength. Seven micrometeorite or space debris impacts occurred at locations which were not in that portion of the sample subjected to greater than 90 percent of the applied stress. As a result of this, the impact events on the sample were not detected in the mechanical strength measurements. The physical form and structure of the impact sites was carefully examined to determine the influence of those events upon stress concentration associated with the impact and the resulting mechanical strength. The size of the impact site, insofar as it determines flaw size for fracture purposes, was examined. Surface topography of the impacts reveals that six of the seven sites display impact melting. The classical melt crater structure is surrounded by a zone of fractured glass. Residual stresses arising from shock compression and from cooling of the fused zone cannot be included in the fracture mechanics analyses based on simple flaw size measurements. Strategies for refining estimates of mechanical strength degradation by impact events are presented.

Wiedlocher, David E.↗
NASA NTRS1971

Annealing effects in plated-wire memory elements. II - Recrystallization in Permalloy films.

Results of grain-size measurements in Permalloy platings suggest that recrystallization is possible at temperatures as low as 200 C, but that it is an extremely heterogeneous process. No worthwhile correlation was found to exist between observed grain size and magnetic dispersion in samples aged in the temperature range from 180 to 230 C. It is suggested that the magnetic aging which occurs under these conditions may be due to some other diffusion-controlled process than recrystallization; a process such as chemical homogenization is tentatively preferred.

Marquardt, S. J.↗
NASA NTRS1995

Physical and Optical/Radiative Characteristics of Small Particles in Tropical Cirrus

Whether cirrus clouds heat or cool the Earth-atmosphere system depends on the relative importance of the cloud shortwave albedo effect and the cloud thermal greenhouse effect. Both an determined by the distribution of ice condensate with cloud particle size. The microphysics instrument package flown aboard the DC-8 In TOGA/COARE included an ice crystal replicator, a 2D Greyscale Cloud Particle Probe and a Forward Scattering Spectrometer Aerosol Probe. In combination. these instruments permitted particle size measurements between 0.5 micrometers and 2.6 mm diameter. Ice crystal replicas were used to validate signals from the electro-optical instruments. Typical results show a prevalence in tropical cirrus clouds of micron-sized particles, in addition to cloud particles that exceed 100 micrometer radius. The mechanism of their formation is growth of (hygroscopic, possibly ocean-derived) aerosol particles along the Kohler curves. The concentration of small particles is higher and less variable in space and time, and their tropospheric residence time is longer, than those of large cloud particles because of lower sedimentation velocities. Small particles shift effective cloud particle radii to sizes much smaller than the mean diameter of the cloud particles. This causes an increase in shortwave reflectivity and IR emissivity. and a decrease in transmissivity. In the cirrus outflow of tropical cyclone Oliver on 8 February, 1993, the reflectivity increases with altitude (decreasing temperature) stronger than does cloud emissivity, yielding enhanced radiative cooling at higher altitudes.

Pueschel, R. F.↗
NASA NTRS2001

A Moderate Resolution View of the Spectral Absorption of Clouds

Some of the first evidence of a cloud absorption anomaly came from retrievals of cloud droplet size using measured multispectral cloud reflectance and in situ microphysical measurements. It was found that spectra computed from the measured droplet size or, equivalently, effective radius inverted from the reflectance measurements disagreed in such a way that suggested there was more absorption in cloud than predicted by theory. During the past decade new evidence of a cloud absorption anomaly has emerged from broadband solar flux measurements from above and below clouds. Based on these findings new field campaigns were devised to specifically address this problem. The most recent of these, the Atmospheric Radiation Measurement (ARM) Enhanced Shortwave Experiment II (ARESEII), included measurements of upwelling and downwelling moderate resolution (10 nm) solar irradiance spectra from above and below cloud. During this talk we will briefly summarize the advantages and limitations of these spectrally resolved measurements compared to the more standard broadband flux. We will focus on cloudy atmosphere results from the ARESEII field study and compare them to theoretical spectra from three independent models.

Pilewskie, Peter↗
NASA NTRS1990

SAM II and lidar aerosol profile comparisons during AASE

The NASA Langley Research Center aerosol lidar system was one of several instruments that flew aboard a DC-8 during the Airborne Arctic Stratospheric Expedition. Several of the Stratospheric Aerosol Measurement II (SAM II) altitude profiles of aerosol extinction were close enough in time and space to allow for intercomparison with the lidar measurements of aerosol backscatter. Comparisons between three SAM II 1.0 micron aerosol extinction profiles and analogous profiles inferred from nearly simultaneous airborne lidar measurements are discussed. The other two comparisons show the first near-simultaneous SAM II/lidar measurements of a polar stratospheric cloud (PSC). The comparison made well within the edge of a relatively homogeneous PSC layer was also good, especially using an extinction-to-backscatter model derived from in situ PSC particle size measurements.

Osborn, M. T.↗
NASA NTRS1987

18 MHz interferometry of Non-Io-C L-bursts

In order to investigate previous discrepancies in source size measurements, 18-MHz interferometric data of L-bursts from a Non-Io-C storm have been collected during the summer of 1986. Variations noted in the fringe visibility of the Jovian L-bursts indicate that the source size changes in time and that the emission region can sometimes be resolved with a relatively modest baseline. The results suggest that all Jovian source sizes are smaller than 10 arcsec (and are possibly smaller than 0.1 arcmin) and that it is more probable that L-burst emission during a Jovian storm will evolve into S-bursts than that S-bursts will become L-bursts.

Phillips, J. A.↗
NASA NTRS2011

In Situ Aerosol Detector

An affordable technology designed to facilitate extensive global atmospheric aerosol measurements has been developed. This lightweight instrument is compatible with newly developed platforms such as tethered balloons, blimps, kites, and even disposable instruments such as dropsondes. This technology is based on detection of light scattered by aerosol particles where an optical layout is used to enhance the performance of the laboratory prototype instrument, which allows detection of smaller aerosol particles and improves the accuracy of aerosol particle size measurement. It has been determined that using focused illumination geometry without any apertures is advantageous over using the originally proposed collimated beam/slit geometry (that is supposed to produce uniform illumination over the beam cross-section). The illumination source is used more efficiently, which allows detection of smaller aerosol particles. Second, the obtained integral scattered light intensity measured for the particle can be corrected for the beam intensity profile inhomogeneity based on the measured beam intensity profile and measured particle location. The particle location (coordinates) in the illuminated sample volume is determined based on the information contained in the image frame. The procedure considerably improves the accuracy of determination of the aerosol particle size.

Vakhtin, Andrei↗
NASA NTRS1992

Deriving the velocity distribution of meteoroids from the measured meteoroid impact directionality on the various LDEF surfaces

Because of spacecraft orbital motion about the Earth, a much higher flux of meteoroids is expected to strike spacecraft surfaces that face in the direction of spacecraft motion (apex direction) than would strike apex facing or trailing edge surfaces. Impact velocities are also higher on apex facing surfaces compared to antapex facing surfaces which futher increases the apex/antapex ratio of spatial density of impact craters of a given size. Measurements of the areal densities of impact craters on the different LDEF surfaces should give important clues about the velocity distribution, and therefore the origins, of meteoroids. Preliminary results appear to support the meteoroid velocity distributions derived by Erickson and by Kessler, which would lead to a mean impact velocity on the LDEF spacecraft of about 19 km/s.

Zook, Herbert A.↗
NASA NTRS2018

A Rain Taxonomy for Degraded Visual Environment Mitigation

This Technical Memorandum (TM) provides a description of a rainfall taxonomy that defines the detailed characteristics of naturally occurring rainfall. The taxonomy is based on raindrop size measurements collected around the globe and encompasses several different climate types. Included in this TM is a description of these rainfall observations, an explanation of methods used to process those data, and resultant metrics comprising the rain taxonomy database. Each of the categories in the rain taxonomy are characterized by a unique set of raindrop sizes that can be used in simulations of electromagnetic wave propagation through a rain medium.

meteorology↗
NASA NTRS1988

Small-droplet spray measurements with a scattered-light scanner

Interacting two-phase flow through pneumatic two-fluid nozzles was investigated to determine the effect of nitrogen gas mass-velocity on the Sauter mean diameter of water sprays produced by the breakup of small diameter liquid-jets in high velocity gas streams. Tests were conducted primarily in the aerodynamic-stripping regime of liquid-jet atomization. It was found that the loss of droplets due to vaporization and dispersion had a marked effect on drop size measurements. A scattered-light scanner, developed at NASA Lewis Research Center was used to measure Sauter mean diameters, D sub 32, as small as 5 microns, which were correlated with nitrogen gas mass-velocity to give the following expression: D(sup -1)(sub 32) = 11.7(rho (sub n) V(sub n))(sup 1.33) where D sub 32 and p(sub n)V(sub n) are given in centimeters and g/sq cm-sec, respectively. The exponent 1.33 is the same as that predicted by atomizing theory for liquid-jet breakup in high velocity gas streams.

Ingebo, Robert D.↗
NASA NTRS1978

Anthropometry

Data on body-size measurement are presented to aid in spacecraft design. Tabulated dimensional anthropometric data on 59 variables for 12 selected populations are given. The variables chosen were those judged most relevant to the manned space program. A glossary of anatomical and anthropometric terms is included. Selected body dimensions of males and females from the potential astronaut population projected to the 1980-1990 time frame are given. Illustrations of drawing-board manikins based on those anticipated body sizes are included.

Mcconville, J. T.↗
NASA NTRS2017

Surveys of Returned ISS Hardware for MMMOD Impacts

Since February 2001, the Hypervelocity Impact Technology (HVIT) group at the Johnson Space Center (JSC) in Houston has performed 35 post-flight inspections on space exposed hardware returned from the International Space Station (ISS). Data on 1,188 observations of micrometeoroid and orbital debris (MMOD) damage have been collected from these inspections. Survey documentation typically includes impact feature location and size measurements as well as microscopic photography (25-200x). Sampling of impacts sites for projectile residue was performed for the largest features. Results of energy dispersive X-ray spectroscopic analysis to discern impactor source are included in the database when available. This paper will focus on two inspections, the Pressurized Mating Adapter 2 (PMA-2) cover returned in 2015 after 1.6 years exposure with 26 observed impact features, and two Airlock shield panels returned in 2010 after 8.75 years exposure with 58 MMOD impacts. Feature sizes from the observed data are compared to predictions using the Bumper 3 risk assessment code.

Hyde, J. L.↗
NASA NTRS2017

Surveys of ISS Returned Hardware for MMOD Impacts

Since February 2001, the Hypervelocity Impact Technology (HVIT) group at the Johnson Space Center in Houston has performed 26 post-flight inspections on space exposed hardware that have been returned from the International Space Station. Data on 1,024 observations of MMOD damage have been collected from these inspections. Survey documentation typically includes impact feature location and size measurements as well as microscopic photography (25-200x). Sampling of impacts sites for projectile residue was performed for the largest features. Results of Scanning Electron Microscopy (SEM) analysis to discern impactor source is included in the database. This paper will summarize the post-flight MMOD inspections, and focus on two inspections in particular: (1) Pressurized Mating Adapter-2 (PMA-2) cover returned in 2015 after 1.6 years exposure with 26 observed damages, and (2) Airlock shield panels returned in 2010 after 8.7 years exposure with 58 MMOD damages. Feature sizes from the observed data are compared to predictions using the Bumper risk assessment code.

Hyde, James↗
NASA NTRS1996

Physical and Optical/Radiative Characteristics of Aerosol and Cloud Particles in Tropical Cirrus: Importance in Radiation Balance

Whether cirrus clouds heat or cool the Earth-atmosphere system depends on the relative importance of the cloud shortwave albedo effect and the cloud thermal greenhouse effect. Both are determined by the distribution of ice condensate with cloud particle size. The microphysics instrument package flown aboard the NASA DC-8 in TOGA/COARE included an ice crystal replicator, a 2D Greyscale Cloud Particle Probe and a Forward Scattering Spectrometer Aerosol Probe. In combination, the electro-optical instruments permitted particle size measurements between 0.5 micrometer and 2.6 millimeter diameter. Ice crystal replicas were used to validate signals from the electrooptical instruments. Both optical and scanning electron microscopy were utilized to analyze aerosol and ice particle replicas between 0.1 micrometer and several 100 micrometer diameter. In first approximation, the combined aerosol-cloud particle spectrum in several clouds followed a power law N alpha D(sup -2.5). Thus, large cloud particles carried most of the condensate mass, while small cloud and aerosol particles determined the surface area. The mechanism of formation of small particles is growth of (hygroscopic, possibly ocean-derived) aerosol particles along the Kohler curves. The concentration of small particles is higher and less variable in space and time, and their tropospheric residence time is longer, than those of large cloud particles because of lower sedimentation velocities. Small particles shift effective cloud particle radii to sizes much smaller than the mean diameter of the cloud particles. This causes an increase in shortwave reflectivity and IR emissivity, and a decrease in transmissivity. Occasionally, the cloud reflectivity increased with altitude (decreasing temperature) stronger than did cloud emissivity, yielding enhanced radiative cooling at higher altitudes. Thus, cirrus produced by deep convection in the tropics may be critical in controlling processes whereby energy from warm tropical oceans is injected to different levels in the atmosphere to subsequently influence not only tropical but mid-latitude climate.

Pueschel, R. F.↗
NASA NTRS1995

Sizing of colloidal particle and protein molecules in a hanging fluid drop

We report non-invasive particle size measurements of polystyrene latex colloidal particles and bovine serum albumin (BSA) protein molecules suspended in tiny hanging fluid drops of 30 micro-Liter volume using a newly designed fiber optic probe. The probe is based upon the principles of the technique of dynamic light scattering (DLS). The motivation for this work comes from growing protein crystals in outer space. Protein crystals have been grown previously in hanging drops in microgravity experiments on-board the space shuttle orbiter. However, obtaining quantitative information on nucleation and growth of the protein crystals in real time has always been a desired goal, but hitherto not achieved. Several protein researchers have shown interest in using DLS to monitor crystal growth process in a droplet, but elaborate instrumentation and optical alignment problems have made in-situ applications difficult. We demonstrate that such an experiment is now possible. Our system offers fast (5 seconds) determination of particle size, utilize safe levels of very low laser power (less than or equal to 0.2 mW), a small scattering volume (approximately 2 x 10(exp -5) cu mm) and high spatial coherence (Beta) values. This is a major step forward when compared to currently available DLS systems.

Ansari, Rafat R.↗