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At least 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Investigation of the influence of the zeta-potential on the filtration rate in the presence of collectors

The value of the zeta-potential does not have an explicit effect, which is expressed by a simple math correlation, on filtration rate when a solution of the tested collector is filtered through a cake prepared under standard conditions from the examined particulate material. The zeta-potential measurements and filtration tests were carried out on silica and galena with solutions contg. a cationic container ANP and Et xanthane, resp. at PH = 6.5, varying concentration of the agent (0-2500 g/ton), and under a vacuum of 100 to 600 mm Hg.

Provirnina, E. V.↗
NASA NTRS1992

Extrapolation procedures in Mott electron polarimetry

In standard Mott electron polarimetry using thin gold film targets, extrapolation procedures must be used to reduce the experimentally measured asymmetries A to the values they would have for scattering from single atoms. These extrapolations involve the dependent of A on either the gold film thickness or the maximum detected electron energy loss in the target. A concentric cylindrical-electrode Mott polarimeter, has been used to study and compare these two types of extrapolations over the electron energy range 20-100 keV. The potential systematic errors which can result from such procedures are analyzed in detail, particularly with regard to the use of various fitting functions in thickness extrapolations, and the failure of perfect energy-loss discrimination to yield accurate polarizations when thick foils are used.

Gay, T. J.↗
NASA NTRS2008

Optical Detection of Formaldehyde

The potential for buildup .of formaldehyde in closed space environments poses a direct health hazard to personnel. The National Aeronautic Space Agency (NASA) has established a maximum permitted concentration of 0.04 ppm for 7 to 180 days for all space craft. Early detection is critical to ensure that formaldehyde levels do not accumulate. above these limits. New sensor technologies are needed to enable real time,in situ detection in a compact and reusable form factor. Addressing this need,research into the use of reactive fluorescent dyes which reversibly bind to formaldehyde (liquid or gas) has been conducted to support the development of a formaldehyde.sensor. In the presence of formaldehyde the dyes' characteristic fluorescence peaks shift providing the basis for an optical detection. Dye responses to formaldehyde exposure were characterized; demonstrating the optical detection of formaldehyde in under 10 seconds and down to concentrations of 0.5 ppm. To .incorporate the dye .in.an optical sensor device requires. a means of containing and manipulating the dye. Multiple form factors using two dissimilar s~bstrates were considered to determine a suitable configuration. A prototype sensor was demonstrated and considerations for a field able sensor were presented. This research provides a necessary first step toward the development of a compact, reusable; real time optical formaldehyde sensor suitable for use in the U.S. space program,

Patty, Kira D.↗
NASA NTRS2010

Gender Differences in Isokinetic Strength after 60 and 90 d Bed Rest

Recent reports suggest that changes in muscle strength following disuse may differ between males and females. PURPOSE: To examine potential gender differences in strength changes following 60 and 90 d of experimental bed rest. METHODS: Isokinetic extensor and flexor strength of the knee (60deg and 180deg/s, concentric only), ankle (30deg/s, concentric and eccentric), and trunk (60deg/s, concentric only) were measured following 60 d (males: n=4, 34.5+/-9.6 y; females: n=4, 35.5+/-8.2 y) and 90 d (males: n=10, 31.4+/-4.8 y; females: n=5, 37.6+/-9.9 y) of 6-degree head-down-tilt bed rest (BR; N=23). Subjects were fed a controlled diet (55%/15%/ 30%, CHO/PRO/FAT) that maintained body weight within 3% of the weight recorded on Day 3 of bed rest. After a familiarization session, testing was conducted 6 d before BR and 2 d after BR completion. Peak torque and total work were calculated for the tests performed. To allow us to combine data from both 60- and 90-d subjects, we used a mixed-model statistical analysis in which time and gender were fixed effects and bed rest duration was a random effect. Log-transformations of strength measures were utilized when necessary in order to meet statistical assumptions. RESULTS: Main effects were seen for both time and gender (p<0.05), showing decreased strength in response to bed rest for both males and females, and males stronger than females for most strength measures. Only one interaction effect was observed: females exhibited a greater loss of trunk extensor peak torque at 60 d versus pre-BR, relative to males (p=0.004). CONCLUSION: Sixty and 90 d of BR induced significant losses in isokinetic muscle strength of the locomotor and postural muscles of the knee, ankle, and trunk. Although males were stronger than females for most of the strength measures that we examined, only changes in trunk extensor peak torque were greater for females than males at day 60 of bed rest

English, K. L.↗
NASA NTRS2012

Widespread Weathered Glass on the Surface of Mars

Low albedo sediments cover >10(exp 7) sq km in the northern lowlands of Mars, but the composition and origin of these widespread deposits have remained ambiguous despite many previous investigations. Here we use near-infrared spectra acquired by the Mars Express OMEGA (Observatoire pour la Mineralogie, l'Eau, les Glaces, et l'Activite') imaging spectrometer to show that these sediments exhibit spectral characteristics that are consistent with both high abundances of iron-bearing glass and silica-enriched leached rinds on glass. This interpretation is supported by observations of low-albedo soil grains with possible rinds at the Phoenix Mars Lander landing site in the northern lowlands. By comparison with the extensive glass-rich dune fields and sand sheets of Iceland, we propose an explosive volcanic origin for these glass-rich sediments. We also propose that the glassy remnant rinds on the sediments are the result of post-depositional alteration, as these rinds are commonly formed in arid terrestrial volcanic environments during water-limited, moderately acidic leaching. These weathered, glass-rich deposits in the northern lowlands are also colocated with the strongest concentrations of a major global compositional surface type previously identified in mid-infrared spectra, suggesting that they may be representative of global processes. Our results provide potential confirmation of models suggesting that explosive volcanism has been widespread on Mars, and also raise the possibilities that glass-rich volcaniclastics are a major source of eolian sand on Mars and that widespread surficial aqueous alteration has occurred under Amazonian climatic conditions.

Horgan, Briony↗
NASA NTRS2021

Sub-city Scale Hourly Air Quality Forecasting by Combining Models, Satellite Observations, and Ground Measurements

While multiple information sources exist concerning surface-level air pollution, no individual source simultaneously provides large-scale spatial coverage, fine spatial and temporal resolution, and high accuracy. It is, therefore, necessary to integrate multiple data sources, using the strengths of each source to compensate for the weaknesses of others. In this study, we propose a method incorporating outputs of NASA’s GEOS Composition Forecasting model system with satellite information from the TROPOMI instrument and ground measurement data on surface concentrations. Although we use ground monitoring data from the Environmental Protection Agency network in the continental United States, the model and satellite data sources used have the potential to allow for global application. This method is demonstrated using surface measurements of nitrogen dioxide as a test case in regions surrounding five major US cities. The proposed method is assessed through cross-validation against withheld ground monitoring sites. In these assessments, the proposed method demonstrates major improvements over two baseline approaches which use ground-based measurements only. Results also indicate the potential for near-term updating of forecasts based on recent ground measurements.

C. Malings↗
NASA NTRS2007

Process for High-Rate Fabrication of Alumina Nanotemplates

An anodizing process, at an early stage of development at the time of reporting the information for this article, has shown promise as a means of fabricating alumina nanotemplates integrated with silicon wafers. Alumina nanotemplates are basically layers of alumina, typically several microns thick, in which are formed approximately regular hexagonal arrays of holes having typical diameters of the order of 10 to 100 nm. Interest in alumina nanotemplates has grown in recent years because they have been found to be useful as templates in the fabrication of nanoscale magnetic, electronic, optoelectronic, and other devices. The present anodizing process is attractive for the fabrication of alumina nanotemplates integrated with silicon wafers in two respects: (1) the process involves self-ordering of the holes; that is, the holes as formed by the process are spontaneously arranged in approximately regular hexagonal arrays; and (2) the rates of growth (that is, elongation) of the holes are high enough to make the process compatible with other processes used in the mass production of integrated circuits. In preparation for fabrication of alumina nanotemplates in this process, one first uses electron-beam evaporation to deposit thin films of titanium, followed by thin films of aluminum, on silicon wafers. Then the alumina nanotemplates are formed by anodizing the aluminum layers, as described below. In experiments in which the process was partially developed, the titanium films were 200 A thick and the aluminum films were 5 m thick. The aluminum films were oxidized to alumina, and the arrays of holes were formed by anodizing the aluminum in aqueous solutions of sulfuric and/or oxalic acid at room temperature (see figure). The diameters, spacings, and rates of growth of the holes were found to depend, variously, on the composition of the anodizing solution, the applied current, or the applied potential, as follows: In galvanostatically controlled anodizing, regardless of the chemical composition of the solution, relatively high current densities (50 to 100 mA/cm2) resulted in arrays of holes that were more nearly regular than were those formed at lower current densities. . The rates of elongation of the holes were found to depend linearly on the applied current density: the observed factor of proportionality was 1.2 (m/h)/(mA/cm2). For a given fixed current density and room temperature, the hole diameters were found to depend mainly on the chemical compositions of the anodizing solutions. The holes produced in sulfuric acid solutions were smaller than those produced in oxalic acid solutions. The arrays of holes produced in sulfuric acid were more ordered than were those produced in oxalic acid. . The breakdown voltage was found to decrease logarithmically with increasing concentration of sulfuric acid. The breakdown voltage was also found to decrease with temperature and to be accompanied by a decrease in hole diameter. The hole diameter was found to vary linearly with applied potential, with a slope of 2.1 nm/V. This slope differs from slopes (2.2 and 2.77 nm/V) reported for similar prior measurements on nanotemplates made from bulk aluminum. The differences among these slopes may be attributable to differences among impurities and defects in bulk and electron-beam-evaporated aluminum specimens.

Myung, Nosang↗
NASA NTRS1986

Studies on cosmogenic nuclides in meteorites with regard to an application as potential depth indicators

Measurements of stable and radioactive spallation products in meteorites allow to investigate their histories, especially with respect to the exposure to galactic cosmic ray particles and the pre-atmospheric size of the object. While the concentrations of spallation products lead to the determination of exposure and terrestrial ages, production rate ratios are characteristic for the location of the sample in the meteorite. So, one of the aims of this investigation on meteorites is to obtain depth indicators from suitable pairs of cosmogenic nuclides. Because of the different depth profiles for nuclide productions it is necessary to determine the concentrations of a larger number of spallation products in aliquots of a single small sample. Such same sample measurements of Be-10 and light noble gases were performed on 15 ordinary chondrites (7 H- and 8 L-chondrites. Be-10 was determined by accelerator mass spectrometry and the noble gases were measured by static mass spectrometry. The results are summarized and discussed.

Sarafin, R.↗
NASA NTRS2015

Aram Chaos: a Long Lived Subsurface Aqueous Environment with Strong Water Resources Potential for Human Missions on Mars

Aram Chaos, Mars is a crater 280 kilometers in diameter with elevations circa. minus 2 to minus 3 kilometers below datum that provides a compelling landing site for future human explorers as it features multiple scientific regions of interest (ROI) paired with a rich extensible Resource ROI that features poly-hydrated sulfates [1]. The geologic history of Aram Chaos suggests several past episodes of groundwater recharge and infilling by liquid water, ice, and other materials [1-3]. The creation of the fractured region with no known terrestrial equivalent may have been caused by melting of deep ice reservoirs that triggered the collapse of terrain followed by catastrophic water outflows over the region. Aram Chaos is of particular scientific interest because it is hypothesized that the chaotic terrain may be the source of water that contributed to the creation of nearby valleys such as Ares Vallis flowing toward Chryse Planitia. The liquid water was likely sourced as groundwater and therefore represents water derived from a protected subsurface environment making it a compelling astrobiological site [2]. The past history of water is also represented by high concentrations of hematite, Fe-oxyhydroxides, mono-hydrated and poly-hydrated sulfates [1, 2]. Poly-hydrated sulfates are likely to contain abundant water that evolves at temperatures below 500 degrees Centigrade thus conferring Aram Chaos a potentially high value for early in-situ resource utilization (ISRU) [4]. The geologic history also calls for future prospecting of deep ice deposits and possibly liquid water via deep drilling. The most recent stratigraphic units in the central part of Aram Chaos are not fractured, and are part of a dome-shaped formation that features bright, poorly-consolidated material that contains both hydrated sulfates and ferric oxides according to OMEGA (Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité) data [5]. These surface material characteristics are preliminary indications of their potential use in civil engineering activities that involve regolith moving and hauling, while further study is needed to assess traverse-ability challenges. The widespread distribution of sulfates is also of interest as a resource for the use of sulfur as a binding compound in regolith-based concrete for constructions. The terrain depressions caused by the rock fracturing events may challenge surface mobility but also suggest the possibility of using such natural features for additional shielding from space radiation and as emplacement of nuclear surface power reactors for the same reason. The high concentration of hematite (up to 16 percent) in some of the smoother recent terrains of the central part of Aram Chaos [2] is a favorable attribute for metal extraction ISRU to create iron-based feedstock for in-situ fabrication of replacement parts or their repairs. Preliminary data on Aram Chaos indicate that it offers a combination of many critical criteria for human missions to the surface of Mars: equatorial region at low Mars Orbiter Laser Altimeter (MOLA), evidence of hydrated minerals over large areas and at high concentrations tied to historic evidence of liquid water over long periods.

Sibille, L.↗
NASA NTRS2018

Machine Learning Application to Atmospheric Chemistry Modeling

Atmospheric chemistry is a high-dimensionality, large-data problem and thus may be suited to machine-learning algorithms. We show here the potential of a random forest regression algorithm to replace the gas-phase chemistry solver in the GEOS-Chem chemistry model. In this proof-of-concept study, we used one month of model output to train random forest regression models to predict the concentrations of each long-lived chemical species after integration based upon the physical and chemical conditions before the chemical integration. The choice of prediction type has a strong impact on the skill of the regression model. We find best results from predicting the change in concentration for very long-lived species and the absolute concentration for shorter lived species. The skill of the machine learning algorithm is further improved by using a family approach for NO and NO2 rather than treating them independently.By replacing the numerical integrator with the random forest algorithm and running this model for one month, we find that the model is able to reproduce many of the features of the reference chemistry simulation. Replacing the integration methodology with a machine learning algorithm has the potential to be substantially faster. There are a wide range of applications for such an approach, e.g. to generate boundary conditions, for use in air quality forecasts or chemical data assimilation systems, etc.

Keller, Christoph A.↗
NASA NTRS1973

The retarding-potential analyzer on Atmosphere Explorer.

A planar retarding-potential analyzer will be included in each of the Atmosphere Explorer (AE) payloads. The primary functions of the instrument are to supply ion-temperature and ion-concentration data, which it will do at least once every 40 km of flight path in the region of interest with an expected accuracy of better than 2%. In addition, the instrument will determine ion-drift velocities and energy spectra of both the thermal and suprathermal electrons. During eclipse, negative-ion concentrations greater than 0.3/cu cm can be detected, though the normal positive-ion sensitivity is approximately 1.5 ions per cu cm. Changes in the ion concentration along the flight path greater than 0.1% can be monitored with a spatial resolution of less than 40 m.

Hanson, W. B.↗
NASA NTRS1974

Geologic hypotheses of Lake Tanganyika region, Zaire, drawn from ERTS imagery

Based on initial work in the Lake Tanganyika area of eastern Zaire, it has been concluded that ERTS imagery is extremely useful for reconnaissance level geologic mapping and analysis in this region of the humid tropics. In particular, ERTS imagery has proven useful for recognizing and mapping regional structural units, for recognizing major structural features, and for arriving at some preliminary hypotheses about the mineral potential of the area. Results so far indicate that ERTS imagery can make a major contribution to the development of the mineral resources of the country. Research has concentrated on applications of ERTS imagery in the field of cartography, geology, forestry, hydrology and agriculture. For the work in geology, a test site was chosen in eastern Zaire on the shore of Lake Tanganyika in the vicinity of the Lukuga River. This area was selected because of its varied geology and the existence of two frames of cloud-free ERTS imagery.

Wolyce, U.↗
NASA NTRS1976

Relationship between ATS-6 spacecraft-charging occurrences and warm plasma encounters

The occurrences in local time of spacecraft-charging and warm plasma events observed by the University of California at San Diego plasma detector on ATS-6 have been examined using data from 40 contiguous orbits. The local time distribution of charging events was found to maximize between local midnight and dawn and was also similar to the distribution of synchronous spacecraft anomalies reported by others. More than half of the charging events had potentials of -50 V or more, and potentials on the order of -1000 V were observed. All of the spacecraft charging events reported in this paper occurred during sunlit conditions. The warm plasma encounters were concentrated in the local noon-to-dusk sector, and the local-time distributions of charging events and warm plasma encounters were found to be anticorrelated.

Reasoner, D. L.↗
NASA NTRS1980

DIAL with heterodyne detection including speckle noise: Aircraft/shuttle measurements of O3, H2O, and NH3 with pulsed tunable CO2 lasers

Atmospheric trace constituent measurements with higher vertical resolution than attainable with passive radiometers are discussed. Infrared differential absorption lidar (DIAL), which depends on Mie scattering from aerosols, has special advantages for tropospheric and lower stratospheric applications and has great potential importance for measurements from shuttle and aircraft. Differential absorption lidar data reduction involves comparing large amplitude signals which have small differences. The accuracy of the trace constituent concentration inferred from DIAL measurements depends strongly on the errors in determining the amplitude of the signals. Thus, the commonly used SNR expression (signal divided by noise in the absence of signal) is not adequate to describe DIAL measurement accuracy and must be replaced by an expression which includes the random coherent (speckle) noise within the signal. A comprehensive DIAL computer algorithm is modified to include heterodyne detection and speckle noise. Examples for monitoring vertical distributions of O3, H2O, and NH3 using a ground-, aircraft-, or shuttle-based pulsed tunable CO2 laser DIAL system are given.

Brockman, P.↗
NASA NTRS1981

A feature of the behavior of He/+/ in the nightside high-latitude ionosphere during equinox

Observations of a hole of ionization in the nightside high-latitude ionosphere during equinox in which He(+) plays an important role in the relative abundance of the ionic constituents are reported. Ion abundance data were obtained during a period of very low magnetic activity from the retarding potential analyzer and magnetic ion mass spectrometer on board AE-D as the satellite passed across the polar region near midnight. Significant decreases in O(+) and H(+) concentrations are observed in the region between 1544 and 1547 UT within the polar cap, accompanied by the rise and dominance of He(+) ions to low altitudes. The dominance of He(+) is attributed to effects on photoproduction of changes in solar zenith angle as the plasma moves from the dayside to the nightside, where it stagnates or resides for periods greater than about 3 hours just poleward of the auroral zone. Model calculations of the physical processes involved in this mechanism are presented which in general tend to fit the observations.

Heelis, R. A.↗
NASA NTRS1985

An airborne lidar instrument for detection of OH using the technique of laser-induced fluorescence

Under suitable laboratory conditions, it has been demonstrated that the laser-induced fluorescence (LIF) measurement technique is sensitive enough to detect single atoms and molecules. This potential sensitivity has provided motivation for the development of this technique for ambient OH measurements. The present paper is concerned with an airborne lidar instrument for measuring OH concentration as used for the NASA GTE/CITE (Global Tropospheric Experiment/Chemical Instrumentation Test and Evaluation) intercomparison experiments during the fall of 1983 and the spring of 1984. A description is given of a working airborne instrument for measurements of OH in ambient air. The detection sensitivity demonstrated in the experiments should be sufficient for routine measurements in areas in which the OH concentration is in the range of high 1,000,000 molecule per cu cm or higher.

Davis, L. I., Jr.↗
NASA NTRS1989

Polar microwave brightness temperatures from Nimbus-7 SMMR: Time series of daily and monthly maps from 1978 to 1987

A time series of daily brightness temperature gridded maps (October 25, 1978 through August 15, 1987) were generated from all ten channels of the Nimbus-7 Scanning Multichannel Microwave Radiometer orbital data. This unique data set can be utilized in a wide range of applications including heat flux, ocean circulation, ice edge productivity, and climate studies. Two sets of data in polar stereographic format are created for the Arctic region: one with a grid size of about 30 km on a 293 by 293 array similar to that previously utilized for the Nimbus-5 Electrically Scanning Microwave Radiometer, while the other has a grid size of about 25 km on a 448 by 304 array identical to what is now being used for the DMSP Scanning Multichannel Microwave Imager. Data generated for the Antaractic region are mapped using the 293 by 293 grid only. The general technique for mapping, and a quality assessment of the data set are presented. Monthly and yearly averages are also generated from the daily data and sample geophysical ice images and products derived from the data are given. Contour plots of monthly ice concentrations derived from the data for October 1978 through August 1987 are presented to demonstrate spatial and temporal detail which this data set can offer, and to show potential research applications.

Comiso, Josefino C.↗
NASA NTRS1990

A test of the galactic origin of gamma-ray bursts

Models in which gamma-ray bursters are young neutron stars may be difficult to reconcile with the apparently isotropic distribution of observed bursts. To justify this statement, the distribution of old neutron stars in the Galaxy was calculated by integrating numerically some 90,000 orbits in the Galactic gravitational potential for up to 10 to the 10th yr. Other calculations included the dipole moment in the angular distribution of neutron stars as a convenient measure of their concentration toward the Galactic center, the quadrupole moment in their angular distribution as a convenient measure of their concentration toward the Galactic plane, and the average value of V/Vmax as a convenient measure of the radial distribution of neutron stars. Models that require accretion from a cold circumstellar disk or from a close companion are only marginally consistent with the isotropic distribution of the observed bursts. Models that require accretion of interstellar matter are ruled out due to a very strong dipole anisotropy. Models that suggest the Galactic halo origin of gamma-ray bursts are briefly discussed. The GRANAT and GRO missions should provide evidence for or against the association of gamma-ray bursts with the Galactic disk neutron stars.

Paczynski, Bohdan↗