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  • 1
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    Comparative functional ultrastructure of two hypersaline submerged cyanobacterial mats - Guerrero Negro, Baja California Sur, Mexico, and Solar Lake, Sinai, Egypt (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The ultrastructure of the submerged microbial mat from the Solar Lake (SL), Egypt, was compared to that of samples from the Guerrero Negro (GN), Mexico, salt pans. The locations and distributions of the main organisms were determined light microscopy, and the corresponding ultrathin sections were examined under TEM; chemical microprofile analyses were carried out on the day of sampling for microscopic studies. Both communities were found to be dominated by Microleus chthonoplastes, although several morphological species found in the GN mat were absent from the SL mat, including the Tropica nigra and the 'big' Microleus chthonoplastes component. The chemical microprofiles of oxygen, sulfide, pH, and the oxygenic photosynthesis in the two mats were virtually identical. In both mats, the photic zone was restricted to the upper 800 microns of the mat, and oxygenic photosynthesis was detected down to 600 microns.
    Keywords: LIFE SCIENCES (GENERAL)
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  • 2
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    Ion-acoustic waves in a plasma with negative ions (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Propagation and damping of ion-acoustic waves have been investigated in a Q-machine plasma consisting of K(+) positive ions, SF6(-) negative ions, and electrons. The phase velocity of the ion-acoustic 'fast' mode increases with increasing epsilon, the concentration of negative ions. The wave damping decreases with increasing epsilon, and nearly disappears, for the highest wave frequencies investigated, when epsilon is more than about 0.9. Both results are in agreement with predictions from Vlasov theory.
    Keywords: PLASMA PHYSICS
    Type: Physics of Fluids B (ISSN 0899-8221); 3; 284-287
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  • 3
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    Electrostatic ion-cyclotron waves in a two-ion component plasma (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The excitation of electrostatic ion cyclotron (EIC) waves is studied in a single-ended Q machine in a two-ion component plasma (Ca+ and K+). Over a large range of relative concentrations of Cs+ and K+ ions, two modes are excited with frequencies greater than the respective cyclotron frequencies of the ions. The results are discussed in terms of a fluid theory of electrostatic ion cyclotron waves in a two-ion component plasma.
    Keywords: PLASMA PHYSICS
    Type: IEEE Transactions on Plasma Science (ISSN 0093-3813); 16; 396-398
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  • 4
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    Transition from moving to stationary double layers in a single-ended Q machine (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Large-amplitude (less than about 100 percent) relaxation oscillations in the plasma potential are known to be generated when the cold endplate of a single-ended Q machine is biased positively. These oscillations are associated with double layers that form near the hot plate (plasma source) and travel toward the endplate at about the ion-acoustic velocity. At the endplate they dissolve and then form again near the hot plate, the entire process repeating itself in a regular manner. By admitting a sufficient amount of neutral gas into the system, the moving double layers were slowed down and eventually stopped. The production of stationary double layers requires an ion source on the high-potential side of the double layers. These ions are provided by ionization of the neutral gas by electrons that are accelerated through the double layer. The dependence of the critical neutral gas pressure required for stationary double-layer formation on endplate voltage, magnetic field strength, and neutral atom mass has been examined. These results are discussed in terms of a simple model of ion production and loss, including ion losses across the magnetic field.
    Keywords: PLASMA PHYSICS
    Type: Physics of Fluids B (ISSN 0899-8221); 2; 1936-194
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  • 5
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    Ion-beam focusing in a double-plasma device (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The authors studied the propagation of a low-energy charge-neutralized ion beam injected into the target region of a long double-plasma device. A magnetic field of up to about 180 G may be applied along the axis of the device. As a result of charge exchange collisions, the ion beam is attenuated as it propagates into the target region. However, under certain conditions of magnetic field strength and neutral gas pressure, the authors have observed a `reemergence' of the beam on axis far downstream in the target. This reemergence of the ion beam is attributed to a focusing of the ions by a self-consistently produced radial ambipolar electric field. The effect may be expected to occur in other types of plasma devices as well, whenever a sufficiently large radially inward electric field is present.
    Keywords: PLASMA PHYSICS
    Type: IEEE Transactions on Plasma Science (ISSN 0093-3813); 16; 590-596
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  • 6
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    Mediterranean Crustal Motions: Numerical Models Constrained by Geologic and Space Geodetic Data (1996)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Keywords: Geophysics
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  • 7
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    High Upward Fluxes of Formic Acid from a Boreal Forest Canopy (2016)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Eddy covariance fluxes of formic acid, HCOOH, were measured over a boreal forest canopy in spring/summer 2014. The HCOOH fluxes were bidirectional but mostly upward during daytime, in contrast to studies elsewhere that reported mostly downward fluxes. Downward flux episodes were explained well by modeled dry deposition rates. The sum of net observed flux and modeled dry deposition yields an upward gross flux of HCOOH, which could not be quantitatively explained by literature estimates of direct vegetative soil emissions nor by efficient chemical production from other volatile organic compounds, suggesting missing or greatly underestimated HCOOH sources in the boreal ecosystem. We implemented a vegetative HCOOH source into the GEOS-Chem chemical transport model to match our derived gross flux and evaluated the updated model against airborne and spaceborne observations. Model biases in the boundary layer were substantially reduced based on this revised treatment, but biases in the free troposphere remain unexplained.
    Keywords: Geophysics
    Type: GSFC-E-DAA-TN47288 , Geophysical Research Letters (ISSN 0094-8276); 43; 17; 9342-9351
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  • 8
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    Intermittent acceleration as a countermeasure to soleus muscle atrophy (1992)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The effectiveness of using intermittent acceleration as a countermeasure to muscle atrophy was investigated in rats subjected to 7 days of hindlimb suspension interrupted by daily periods of 1.2 g acceleration, for 15-min periods evenly spaced over 12-hr interval. It was found that this regimen, when repeated for 7 days, failed to completely maintain the mass of soleus muscle, which was 84 percent of control.
    Keywords: LIFE SCIENCES (GENERAL)
    Type: Journal of Applied Physiology (ISSN 8750-7587); 72; 428-433
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  • 9
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    Two Years of Chemical Sampling on Meridiani Planum by the Alpha Particle X-Ray Spectrometer Onboard the Mars Exploration Rover Opportunity (2006)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: For over two terrestrial years, the Mars Exploration Rover Opportunity has been exploring the martian surface at Meridiani Planum using the Athena instrument payload [1], including the Alpha Particle X-Ray Spectrometer (APXS). The APXS has a small sensor head that is mounted on the robotic arm of the rover. The chemistry, mineralogy and morphology of selected samples were investigated by the APXS along with the Moessbauer Spectrometer (MB) and the Microscopic Imager (MI). The Rock Abrasion Tool (RAT) provided the possibility to dust and/or abrade rock surfaces down to several millimeters to expose fresh material for analysis. We report here on APXS data gathered along the nearly 6-kilometers long traverse in craters and plains of Meridiani.
    Keywords: Geophysics
    Type: 37th Lunar and Planetary Science Conference; Mar 13, 2006 - Mar 17, 2006; South Shore harbor, League City, Texas; United States
    Format: application/pdf
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  • 10
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    Plasma density fluctuations observed during Space Shuttle Orbiter water releases (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Observations by the Langmuir probe on the Plasma Diagnostics Package flown as part of the Spacelab 2 mission in the summer of 1985 show a strong increase in the level of turbulence near the Shuttle Orbiter during operations in which liquid water is released. The spectrum of the plasma density fluctuations peaks at the lowest frequencies measured (a few Hz) and extends up to a few kHz, near the lower hybrid frequency. Two potential mechanisms for generating the plasma turbulence are suggested which are both based on the production of water ions as a result of charge exchange with the ambient oxygen ions in the ionosphere. The first mechanism proposed is the ion-plasma instability which arises from the drift of the contaminant with respect to the ambient oxygen ions. The other mechanism proposed is the Ott-Farley instability, which is a result of the ring distribution formed by the 'pick-up' water ions.
    Keywords: PLASMA PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 94; 12081-12
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