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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Starspots found on the ellipsoidal variable V350 lacertae = HR 8575

It has been a puzzle why this chromospherically active, strong-dynamo K2 IV-III star is not known to have the large starspots characteristic of other such stars. Published individual radial velocities, which had never been analyzed, are used to derive an orbital solution. Combined with the one older existing orbital solution, this yields an improved orbital ephemeris: time of conjunction (K star behind) = JD 2445255.47 +/- 0.11 days and period = 17.75346 +/- 0.00016 days. All available photoelectric photometry, from 1970.9 to 1992.5, is collected A cos 2 theta fit of the ellipticity effect yields JD 2445255.60 +/- 0.06 days for a time of conjunction, 17.7523 +/- 0.0005 days for the period, and 0.084 mins for the peak-to-peak amplitude in V. With the ellipticity effect removed, the light curve does show measurable starspot variability in 15 of 16 data groups, the starspot wave amplitudes ranging between 0.03 mins and 0.08 mins. Ten starspots are identified and their rotation periods determined, the mean being 17.70 +/- 0.03 days (confirming synchronous rotation) and the range being Delta P/P = 0.017 +/- 0.006 (indicating differential rotation). There is a slow variation in mean brightness, almost 0.1 min in range and at least 2 decades in length.

Crews, Lionel J.↗
NASA NTRS1975

Certain problems in the development and design of scintillation and Cerenkov counters

The feasibility is examined of increasing the effectiveness of the scintillation and Cerenkov counters through improving light collection of the recorded radiation on the photoelectric cathode of the photomultiplier. An example of how to select a detector of the directional plexiglas Cerenkov counter is given. Also presented are experimentally obtained amplitude distributions during the recording of cosmic ray muons. The necessity to obtain agreement between the characteristic spectrum of the photocathode of the photomultiplier and the spectrum of the recorded radiation is stressed.

Chukin, V. S.↗
NASA NTRS1983

Modification of the photoionization of hydrogen by a low-frequency laser

The modification of the photoionization cross section due to the presence of an intense low-frequency laser is obtained for the hydrogen-atom target. Previous calculations of this effect have neglected the effects of the Coulomb potential in the final state. A sum rule was obtained which indicates that the photoelectric current is unaffected by the presence of the low-frequency laser to lowest order in the laser frequency. It is found that the Coulomb potential changes this result and that the photoelectric current is changed by a factor which depends upon the laser parameters and the electron momentum. A simple experiment is suggested to confirm this prediction.

Fiordilino, E.↗
NASA NTRS1979

Photoabsorption cross sections of CH3F, CHF3, CH3Cl, and CF2Cl2 from 175 to 760 A

The study of fluorinated and chlorinated hydrocarbons is of great interest because of their suspected effect on the ozone layer in the atmosphere. Using synchrotron radiation as a continuum background, the present study measures photoelectrically the photoabsorption cross sections of CH3F, CHF3, CH3Cl, and CF2Cl2 in the 175-760 A (70.8-16.3 eV) region, using a double ionization chamber. The absolute absorption cross sections and a tentative interpretation of the observed discrete structures are presented.

Wu, C. Y. R.↗
NASA NTRS1977

Facular line profiles and facular models

Profiles for lines near 5250 A have been calculated from facular models and compared with observed profiles. The observations are from photographic and photoelectric spectra. The atomic parameters are determined by comparison of calculated profiles with those observed for the quiet sun. The effects of finite spatial resolution and a magnetic field are required to obtain agreement with observed facular line profiles. The empirical magnetic field deduced by matching observed and calculated profiles is reasonably consistent with that in the facular models. The main purpose of this paper is to show that by including the effects of scattered photospheric light and a strong magnetic field, reasonable agreement can be achieved between observed and calculated facular line profiles. Results are also presented for the wing of the Ca II K line, showing line profiles and effective filtergram contrasts for several facular models. It is concluded that observations made with weak Fraunhofer lines are not very useful for discrimination among facular models, particularly without simultaneous magnetic-field measurements. The K line may offer a better discriminator. The facular model presently favored has a magnetic field strength of about 1500 gauss at the surface of the photosphere.

Chapman, G. A.↗
NASA NTRS1976

A real-time optical data processing device

A novel liquid-crystal electro-optical device useful as a real-time input device in coherent optical data processing is described. The device is a special adaptation of an ac photoactivated liquid-crystal light valve, and utilizes a hybrid field effect (45 deg twisted nematic effect in OFF state and pure optical birefringence of the liquid crystal in ON state). A thin-film sandwich exerts photoelectric control over the optical birefringence of a thin liquid-crystal layer. Liquid-crystal layer thickness is successfully reduced without image degradation. The device offers high resolution (better than 100 lines/mm), contrast (better than 100/1), high speed (10 msec ON, 15 msec OFF), high input sensitivity, low power input, low fabrication cost, and can be operated at below 10 V rms. Preliminary measurements on device performance in level slicing, filtering, contrast reversal, and edge enhancement are under way.

Jacobson, A.↗
NASA NTRS1999

Behavior of Windblown Sand on Mars: Results from Single-Particle Experiments

Experiments are investigating the behavior of individual sand grains in the high-energy martian aeolian regime. Energy partitioning during impact of a saltating grain determines grain longevity, but it also influences the way in which the bed becomes mobilized by reptation. When single grains of sand are fired into loose beds, the bed can absorb up to 90% of the impact energy by momentum transfer to other grains; it has been discovered that the impacting grains cause circular craters even at low impact angles. Hundreds of grains can be splashed by a single high-velocity (100 m/s) impact causing more bed disturbance through reptation than previously thought. The research is supported by NASA's PG&G Program. Because the martian aeolian environment in both high energy and of long duration, the most mobile fractions of windblown sand should have eradicated themselves by attrition, unless sand supply has kept pace with destruction. It is therefore important to understand the rate of grain attrition in order to make sense of the existence of vast dune fields on Mars. Attrition, has been addressed in other studies, but precise data for a single saltating grain striking a loose bed of sand have not been acquired -- the quintessential case to be understood for dunes on Mars. To acquire these data, we are employing a compound crossbow which has the bolt-firing mechanism replaced with a pneumatically-automated sabot system. The sabot can launch individual grains of sand of any size between several millimeters and about 50 microns, at velocities up to 100m/s. This is around the maximum velocity expected for saltating grains on Mars. The sabot sled is equipped with photoelectric sensors for measuring shot velocity. Baffling of the grain's exit orifice has enabled projection of single grains without significant aerodynamic effects from the sabot. Grains are fired into loose beds of sand at about 15 degrees from the horizontal (typical saltation trajectory at impact) while being filmed on high-speed video. High-intensity pulse illumination for the grains is triggered by the solenoid-operated bow trigger. A 45 degree mirror over the impact site provides simultaneous horizontal and vertical images of the impact on each video frame. UV fluorescence is enabling grain and grain-fragment recovery. At 100 m/s, grains of all sizes shatter into many fragments when the sand is replaced with a solid target. Kinetic energy of the grains at this velocity exceeds the critical energy for catastrophic failure of minerals. Although probably exceptional as a grain speed, it suggests that conditions on Mars might elevate materials into an attrition regime not encountered on other planets; individual grains blown across rock pavements on Mars will have short lifespans. When experimental grains impact loose (dune) sand, much, if not most of the kinetic energy is converted into momentum of other grains. Using high-speed filming, the energy involved in splashing grains at the impact site can be derived from the size of the crater, the speed of the splashed grains, and the rebound speed of the impactor. The amount of energy partitioned into material failure (as opposed to momentum) is too small a fraction of the total to be calculated under these circumstances. This does not necessarily mean that little damage occurs to the grains (the full extent of the damage has yet to be determined) because only a small fraction of the impact energy is required for inducing brittle fracture. Damage is orders of magnitude less than during impact against solid surfaces.

Marshall, J. R.↗
NASA NTRS1981

The diameter of Juno from its occultation of AG + 0 deg 1022

The occultation on Dec. 11, 1979, of AG + 0 deg 1022 by Juno was observed photoelectrically from 15 sites distributed across the occultation track. The observations are well represented by a mean elliptical limb profile having semimajor and semiminor axes of 145.2 + or 0.8 and 122.8 + or - 1.9 km, respectively. The corresponding effective diameter of Juno is 267 + or - 5 km, where the uncertainty has been conservatively increased to reflect the presence of limb irregularities clearly seen in the observations. Published radiometric and polarimetric diameters for Juno are 6% to 7% smaller than the occultation result. No secondary occultations attributable to possible satellites of Juno were recorded at any of 23 photoelectrically equipped observing sites.

Millis, R. L.↗
NASA NTRS2008

Electrostatic Charging of Lunar Dust by UV Photoelectric Emissions and Solar Wind Electrons

The ubiquitous presence of dust in the lunar environment with its high adhesive characteristics has been recognized to be a major safety issue that must be addressed in view of its hazardous effects on robotic and human exploration of the Moon. The reported observations of a horizon glow and streamers at the lunar terminator during the Apollo missions are attributed to the sunlight scattered by the levitated lunar dust. The lunar surface and the dust grains are predominantly charged positively by the incident UV solar radiation on the dayside and negatively by the solar wind electrons on the night-side. The charged dust grains are levitated and transported over long distances by the established electric fields. A quantitative understanding of the lunar dust phenomena requires development of global dust distribution models, based on an accurate knowledge of lunar dust charging properties. Currently available data of lunar dust charging is based on bulk materials, although it is well recognized that measurements on individual dust grains are expected to be substantially different from the bulk measurements. In this paper we present laboratory measurements of charging properties of Apollo 11 & 17 dust grains by UV photoelectric emissions and by electron impact. These measurements indicate substantial differences of both qualitative and quantitative nature between dust charging properties of individual micron/submicron sized dust grains and of bulk materials. In addition, there are no viable theoretical models available as yet for calculation of dust charging properties of individual dust grains for both photoelectric emissions and electron impact. It is thus of paramount importance to conduct comprehensive measurements for charging properties of individual dust grains in order to develop realistic models of dust processes in the lunar atmosphere, and address the hazardous issues of dust on lunar robotic and human missions.

Abbas, Mian M.↗
DOE OSTI2021

Silicate minerals as a direct source of limiting nutrients: Siderophore synthesis and uptake promote ferric iron bioavailability from olivine and microbial growth

Iron is a micronutrient critical to fundamental biological processes including respiration and photosynthesis, and it can therefore impact primary and heterotrophic productivity. Yet in oxic environments, iron is highly insoluble, rendering it, in principle, unavailable as a nutrient for biological growth. Life has “solved” this problem via the invention of iron chelates, known as siderophores, that keep iron available for microbial productivity. In this work, we examined the impact of siderophore synthesis on the speciation, mobility, and bioavailability of iron from rock-forming silicate minerals—shedding new light on the mechanisms by which microbes use mineral substrates to support primary productivity, as well as the consequent effects on silicate dissolution. Growth experiments were performed with Shewanella oneidensis MR-1 in an oxic, iron-depleted minimal medium, amended with olivine minerals as the sole source of iron. Experiments included the wild-type strain MR-1, and a siderophore synthesis gene deletion mutant strain (ΔMR-1). Relative to MR-1, ΔMR-1 exhibited a very pronounced growth penalty and an extended lag phase. However, substantial growth of ΔMR-1, comparable to MR-1 growth, was observed when the mutant strain was provided with siderophores in the form of either filtrate from a well-grown MR-1 culture, or commercially available deferoxamine. These observations suggest that siderophores are critical for S. oneidensis to acquire iron from olivine. Growth-limiting concentrations of deferoxamine amendments were observed to be ≤5–10 µM, concentrations significantly lower than previously recorded as necessary to impact mineral dissolution rates. X-ray photoelectric spectroscopy analyses of the incubated olivine surfaces suggest that siderophores deplete mineral surface layers of ferric iron. Combined, these results demonstrate that low micromolar concentrations of siderophores can effectively mobilize iron bound within silicate minerals, supporting very significant biological growth in limiting environments. The specific mechanism would involve siderophores removing a protective layer of nanometer-thick iron oxides, enhancing silicate dissolution and nutrient bioavailability.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1986

On the completeness of the Medium Sensitivity Survey quasar sample

The Medium Sensitivity Survey (MSS) quasar sample is being used more and more to study quasar properties in general and to analyze the relationship between X-ray-selected and optically selected quasars in particular. These studies have recently shown that current knowledge of the properties of optically selected quasars (luminosity function, evolution, X-ray to optical luminosity ratio) leads to the prediction that many more X-ray-selected quasars should have been detected than are actually observed. Prompted by this fact, a detailed examination of possible causes of incompleteness of the MSS quasar sample has been undertaken, paying particular attention to the problem of photoelectric absorption due to the interstellar medium within the Galaxy. It is found that there is no evidence of a loss of sources due to the effects considered, and that the MSS quasar sample is statistically complete.

Maccacaro, T.↗
NASA NTRS2017

Herschel Extreme Lensing Line Observations: [CII] Variations in Galaxies at Redshifts z=1-3*

We observed the [C II] line in 15 lensed galaxies at redshifts 1 less than z less than 3 using HIFI on the Herschel Space Observatory and detected 14/15 galaxies at 3sigma or better. High magnifications enable even modestly luminous galaxies to be detected in [C II] with Herschel. The [C II] luminosity in this sample ranges from 8 × 10(exp 7) solar luminosity to 3.7 × 10(exp 9) solar luminosity (after correcting for magnification), confirming that [C II] is a strong tracer of the ISM at high redshifts. The ratio of the [C II] line to the total far-infrared (FIR) luminosity serves as a measure of the ratio of gas to dust cooling and thus the efficiency of the grain photoelectric heating process. It varies between 3.3% and 0.09%. We compare the [C II]/FIR ratio to that of galaxies at z = 0 and at high redshifts and find that they follow similar trends. The [C II]/FIR ratio is lower for galaxies with higher dust temperatures. This is best explained if increased UV intensity leads to higher FIR luminosity and dust temperatures, but gas heating does not rise due to lower photoelectric heating efficiency. The [C II]/FIR ratio shows weaker correlation with FIR luminosity. At low redshifts highly luminous galaxies tend to have warm dust, so the effects of dust temperature and luminosity are degenerate. Luminous galaxies at high redshifts show a range of dust temperatures, showing that [C II]/FIR correlates most strongly with dust temperature. The [C II] to mid-IR ratio for the HELLO sample is similar to the values seen for low-redshift galaxies, indicating that small grains and PAHs dominate the heating in the neutral ISM, although some of the high [CII]/FIR ratios may be due to turbulent heating.

Malhotra, Sangeeta↗
NASA NTRS1996

Operation Closed-Loop Observation Scheduling and Execution

In this paper, we present a fully operational system that performs closed-loop observation scheduling and execution and has been in daily use on an automatic photoelectric telescope at the Fairborn Observatory on Mt. Hopkins in Arizona. The scheduler is part of the Associate Principal Astronomer system that also provides tools that enable the effective management of automatic telescopes. The paper describes the flexible schedule representation used and describes how the uncertainties and errors inherent in the domain are handled.

Bresina, John↗
NASA NTRS2014

Concerning the Charging of an Exploration Craft on and near a Small Asteroid

Introduction: An object immersed in an airless plasma environment will experience a natural process of surface charging in order to acheieve current balance, or zero net electric current to the object. It has been shown in recent computer simulations that the small-body plasma environment is very complex [1], considering effects of photoemission, topography, and formation of a plasma wake. For this work we consider an exploration craft (or astronaut) immersed within a plasma environment near an asteroid, which exhibits widely varying solar wind and photoelectric particle fluxes and continuously evolving illumination conditions. Objective: We aim to determine how an explo-ration craft or astronaut suit accumulates charge while located in the "nightside" asteroid wake where the particle fluxes are reduced, and in the dayside near-surface photoelectron sheath, by combining an object charging model [2] with kinetic simulations of a near-asteroid plasma environment [1]. We consider an astronaut floating near the asteroid while not in contact with the surface, as well as an astronaut moving along the surface using their hands/gloves to crawl along. Results: The modeling results suggest that remediation of triboelectric charge via accumulation of plasma currents is an important factor to consider when designing future NEA mission infrastructure, especially if repeated and frequent contact with the surface is planned. In shadowed regions such as the location shown in Fig. 1a, the plasma currents are so low (and the effective charge-remediation timescale so long, e.g. minutes to hours) that repeated contact with the surface tribocharges the glove in an uncontrollable fashion, as shown for two representative electron temperatures in Fig. 2a. The resulting buildup of significant negative charge would eventually initiate some other "current of last resort" [4] such as transport of positively-charged dust, field-emission from the glove, or significant alteration of environmental ion currents within the wake. In contrast, the few-meters-thick dayside photoelectron sheath in which the astronaut of Fig. 1b is immersed in is so rich in electrons (and hence so electrically conductive) that accumulated tribocharge dissipates almost instantaneously (e.g. in less than a ms) as shown in Fig. 2b. As our model astronaut orbits the NEA they would experience plasma currents and associated charge re-mediation times spanning many orders of magnitude, and the fusion between our numerical models provides a detailed understanding of the charging hazards possibly associated with contact-based NEA exploration.

Asteroid↗
NASA NTRS1977

Extreme ultraviolet spectrograph ATM experiment S082B

The extreme-ultraviolet double-dispersion photographic spectrograph for the Apollo Telescope Mount (ATM) experiment S082B on Skylab is described. Novel features were the use of a predisperser grating with a ruling whose spacing varied approximately linearly with distance for the purpose of increasing the instrument speed by reducing the astigmatism and a photoelectric servosystem to stabilize to 1 sec of arc the solar image at various near-limb positions. The 970-3940-A range was covered in two sections with effective resolving power of approximately 30,000 from 1100 A to 1970 A. The spatial resolution was 2 x 60 solar sec of arc. During the Skylab mission 6400 exposures were made with the instrument pointed by an astronaut at selected and recorded solar positions.

Bartoe, J.-D. F.↗
NASA NTRS2021

Detection of Anomalies in the UV/Vis Reflectances from the Ozone Monitoring Instrument

Various instrumental or geophysical artifacts, such as saturation, stray light, or obstruction of light (either coming from the instrument or related to solar eclipses), negatively impact satellite measured ultraviolet and visible Earthshine radiance spectra and downstream retrievals of atmospheric and surface properties derived from these spectra. In addition, excessive noise such as from cosmic ray impacts, prevalent within the South Atlantic Anomaly, can also degrade satellite radiance measurements. Saturation specifically pertains to observations of very bright surfaces such as sun glint over open water or thick clouds. When saturation occurs, additional photoelectric charge generated at the saturated pixel may overflow to pixels adjacent to a saturated area and be reflected as a distorted image in the final sensor output.When these effects cannot be corrected to an acceptable level for science quality retrievals, flagging of the affected pixels is indicated. Here, we introduce a straightforward detection method that is based on the correlation, r, between the observed Earthshine radiance and solar irradiance spectraover a 10 nm-spectral range; our Decorrelation Index (DI for brevity) is simply defined as DI=1-r. DI increases with anomalous additive effects or excessive noise in either radiances, the most likely cause indata from theOzone Monitoring Instrument (OMI),or irradiances. DI is relatively straight-forward to use and interpret and can be 20computed for different wavelength intervals. We developed a set of DIs for two spectral channelsof the OMI, a hyperspectral pushbroom imaging spectrometer. For each OMI spatial measurement, we define 14 wavelength-dependent DIs within the OMI visible channel (350-498 nm) and 6 DIs in its ultraviolet 2 (UV2) channel (310-370 nm). As defined, DIs reflect a continuous range of deviations of observed spectra from the reference irradiance spectrum that are complementary to the binary Saturation Possibility Warning (SPW) flags currently provided for each individual spectral/spatial pixel in the OMI radiance data set. Smaller values of DI are also caused by a number of geophysical factors; this allows one to obtain interesting physical results on the global distribution of spectral variations.

Space sensor↗