Bed forms in base-surge deposits - Lunar implications.
Undulating dunelike deposits of surface debris similar to base-surge deposits in maar volcanoes and tuff rings, discussing underground ice existence
Fisher, R. V.↗
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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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Multimegawatt MPD thruster design considerations
Performance and lifetime requirements for multimegawatt magnetoplasmadynamic (MPD) thrusters were used to establish a baseline 2.5 MW thruster design. The chamber surface power deposition resulting from current conduction, plasma and surface radiation, and conduction from the hot plasma was then evaluated to establish the feasibility of thruster operation. It was determined that state of the art lithium heat pipes were adequate to cool the anode electrode, and that the liquid hydrogen propellant could be used to cool the applied field magnet, cathode, and backplate. Unresolved issues having an impact of thruster design are discussed to help focus future research.
Myers, Roger M.↗
Comprehensive Modeling of Superficial Dust Removal via Electrostatic and Dielectrophoretic Forces in Extraterres-trial Exploration Mission
The Electrostatics and Surface Physics Laboratory (ESPL) at NASA Kennedy Space Center has developed a dust mitigation technology that uses electrostatic and dielectrophoretic (DEP) forces to disperse and remove the dust already deposited on surfaces preventing the accumulation of dust particles approaching or already deposited on those surfaces.
Dominguez, Jesus A.↗
Method of enhancing a DLC coated surface for enhanced multipaction resistance
A method for creating an enhanced multipaction resistant diamond-like coating (DLC) coating with lower Secondary Electron Emission (SEE) properties is performed on an initial surface by etching a DLC coating deposited on the surface after deposition and optionally creating interlayers to enhance adhesion mechanical properties between the DLC coating and the initial surface.
Nichol, Robert Michael↗
Acid dew and the role of chemistry in the dry deposition of reactive gases to wetted surfaces
A formalism is developed to describe the dry deposition of soluble reactive gases to wetted surfaces in terms of the relevant meteorological conditions, the surface roughness, the total amount of liquid water present on the surface, the rate of accumulation of this water, and the species' solubility and reactivity in the surface water. This formulation is then incorporated into a model designed to simulate the generation of acidic dew from the deposition of HNO3, SO2, S(IV) oxidants, H2O2, and O3. Similar to the observations of dew in the continental U.S., the model generates a dewdrop pH of about 4 by the end of the night; the pH can rapidly fall to toxic levels due to rapid evaporation after sunrise. Relatively low deposition velocities are predicted for the SO2 and O3 because of their lower solubilities and hence larger surface resistances than those of the other oxidants. Because the chemical lifetime of the SO2 in the dew is influenced by the atmospheric levels of H2O2, O3, and SO2, the SO2 deposition velocity is a strong function of these species' atmospheric abundances.
Chameides, William L.↗
Global Simulation of Atmospheric Mercury Concentrations and Deposition Fluxes
Results from a numerical model of the global emissions, transport, chemistry, and deposition of mercury (Hg) in the atmosphere are presented. Hg (in the form of Hg(O) and Hg(II)) is emitted into the atmosphere from natural and anthropogenic sources (estimated to be 4000 and 2100 Mg/ yr, respectively). It is distributed between gaseous, aqueous and particulate phases. Removal of Hg from the atmosphere occurs via dry deposition and wet deposition, which are calculated by the model to be 3300 and 2800 Mg/ yr, respectively. Deposition on land surfaces accounts for 47% of total global deposition. The simulated Hg ambient surface concentrations and deposition fluxes to the Earth's surface are consistent with available observations. Observed spatial and seasonal trends are reproduced by the model, although larger spatial variations are observed in Hg(O) surface concentrations than are predicted by the model. The calculated atmospheric residence time of Hg is -1.7 years. Chemical transformations between Hg(O) and HG(II) have a strong influence on Hg deposition patterns because HG(II) is removed faster than Hg(O). Oxidation of Hg(O) to HG(II) occurs primarily in the gas phase, whereas HG(II) reduction to Hg(O) occurs solely in the aqueous phase. Our model results indicated that in the absence of the aqueous reactions the atmospheric residence time of Hg is reduced to 1.2 from 1.7 years and the Hg surface concentration is -25% lower because of the absence of the HG(II) reduction pathway. This result suggests that aqueous chemistry is an essential component of the atmospheric cycling of Hg.
Shia, Run-Lie↗
Influence of Dynamic Ozone Dry Deposition on Ozone Pollution
Identifying the contributions of chemistry and transport to observed ozone pollution using regional‐to‐global models relies on accurate representation of ozone dry deposition. We use a recently developed configuration of the NOAA GFDL chemistry‐climate model – in which the atmosphere and land are coupled through dry deposition—to investigate the influence of ozone dry deposition on ozone pollution over northern midlatitudes. In our model, deposition pathways are tied to dynamic terrestrial processes, such as photosynthesis and water cycling through the canopy and soil. Small increases in winter deposition due to more process‐based representation of snow and deposition to surfaces reduce hemispheric‐scale ozone throughout the lower troposphere by 5–12 ppb, improving agreement with observations relative to a simulation with the standard configuration for ozone dry deposition. Declining snow cover by the end of the 21st‐century tempers the previously identified influence of rising methane on winter ozone. Dynamic dry deposition changes summer surface ozone by −4 to +7 ppb. While previous studies emphasize the importance of uptake by plant stomata, new diagnostic tracking of depositional pathways reveals a widespread impact of nonstomatal deposition on ozone pollution. Daily variability in both stomatal and nonstomatal deposition contribute to daily variability in ozone pollution. Twenty‐first century changes in summer deposition result from a balance among changes in individual pathways, reflecting differing responses to both high carbon dioxide (through plant physiology versus biomass accumulation) and water availability. Our findings highlight a need for constraints on the processes driving ozone dry deposition to test representation in regional‐to‐global models.
dry deposition↗
Evaluation of a Robust, In-Situ Surface Treatment for Pipeline Solids Deposition Mitigation in Flowing Systems
Abstract The formation/precipitation and deposition of pipeline solids, such as gas hydrates, asphaltenes, and waxes have long plagued production fields. Given the vast differences in chemistries of these solids, any current prevention or mitigation strategy, particularly for cases where multiple issues are a concern, is likely to involve an extensive assortment of undefined chemical additives that are both costly and add complexity to the system. Surface treatments (coatings), on the other hand, present a relatively new viable option for management strategies. A chemically and physically robust surface treatment with the ability to address deposition issues for multiple pipeline solids could not only decrease the operating expenditures for a field through material cost savings and obviation of downstream separation, but could also simplify produced fluids by eliminating additional chemicals from the mixture. The purpose of this study is to explore the feasibility of a particular surface treatment as part of a solids management strategy. This work utilizes an omniphobic surface treatment to probe its effects on gas hydrate, asphaltene, and wax deposition. Specifically, high pressure rocking cells are employed to study gas hydrate nucleation and deposition. A bench-scale flowloop filled with crude oil and heptane is used to quantify the deposition of crude oil and asphaltenes after a set time period. Lastly, a mechanical shear device measures the adhesion force of wax deposits on untreated/treated surfaces. The gas hydrate rocking cell tests demonstrate an increase in induction time and occasional elimination of hydrate nucleation with the surface treatment. Moreover, the same apparatus indicates that the critical shear to avoid hydrate deposition may be lowered in the presence of the surface treatment compared to untreated pristine carbon steel coupons. A custom-built asphaltene flowloop then establishes that this surface treatment is effective in dramatically reducing the deposition of the aliphatic components of a crude oil, with a moderate reduction in the asphaltene fraction. Finally, mechanical adhesion force measurements for solidified paraffin wax display trends in agreement with the asphaltene results. The surface treatment on both pristine and corroded surfaces is able to reduce the adhesion of wax deposits to values below a pristine, untreated surface.
03 NATURAL GAS↗
Surface Chemistry, Friction, and Wear Properties of Untreated and Laser-Annealed Surfaces of Pulsed-Laser-Deposited WS(sub 2) Coatings
An investigation was conducted to examine the surface chemistry, friction, and wear behavior of untreated and annealed tungsten disulfide (WS2) coatings in sliding contact with a 6-mm-diameter 440C stainless-steel ball. The WS2 coatings and annealing were performed using the pulsed-laser-deposition technique. All sliding friction experiments were conducted with a load of 0.98 N (100 g), an average Hertzian contact pressure of 0.44 GPa, and a constant rotating speed of 120 rpm. The sliding velocity ranged from 31 to 107 mm/s because of the range of wear track radii involved in the experiments. The experiment was performed at room temperature in three environments: ultrahigh vacuum (vacuum pressure, 7X(exp -10) Pa), dry nitrogen (relative humidity, less than 1 percent), and humid air (relative humidity, 15 to 40 percent). Analytical techniques, including scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX), x-ray photo electron spectroscopy (XPS), surface profilometry, and Vickers hardness testing, were used to characterize the tribological surfaces of WS2 coatings. The results of the investigation indicate that the laser annealing decreased the wear of a WS2 coating in an ultrahigh vacuum. The wear rate was reduced by a factor of 30. Thus, the laser annealing increased the wear life and resistance of the WS2 coating. The annealed WS 2 coating had a low coefficient of friction (less than O.1) and a low wear rate ((10(exp -7) mm(exp 3)/N-m)) both of which are favorable in an ultrahigh vacuum.
Miyoshi, Kazuhisa↗
High-energy electron-beam deposition onto a hot graphite surface.
The momentum transfer and blow-off vapor yield resulting from the deposition of a pulsed high-power electron beam onto a plane graphite target with surface temperatures of 300 K and 5000 K are examined experimentally. The results show that with identical electron beams the momentum transfer and vapor yield are between two and three times larger when irradiating the 5000 K surface as compared with the 300 K surface.
Robin, J. E.↗
LANDSAT Study of Alteration Aureoles in Surface Rocks Overlying Petroleum Deposits
The author has identified the following significant results. A series of low altitude underflight remote sensing experiments were flown at Cement and Davenport oil fields, Oklahoma. An experimental algorithm which employs a sinusoidal stretch of brightness values was developed and applied to a January 1973 scene (bands 4, 5, and 6) of Cement. The results, although not spectacular, are extremely encouraging and for the first time demonstrate that the alteration anomaly at Cement may be defined through enhanced LANDSAT images.
Donovan, T. J.↗
LANDSAT study of alteration aureoles in surface rocks overlying petroleum deposits
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Donovan, T. J.↗
Evidence of translations and rotations of gold crystallites vacuum deposited on /111/ MgO surfaces at room temperature
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Metois, J. J.↗
Formation of a pn junction on an anisotropically etched GaAs surface using metalorganic chemical vapor deposition
A continuous p-type GaAs epilayer has been deposited on an n-type sawtooth GaAs surface using MOCVD. A wet chemical etching process was used to expose the intersecting (111)Ga and (-1 -1 1)Ga planes with 6-micron periodicity. Charge-collection microscopy was used to verify the presence of the pn junction thus formed and to measure its depth. The ultimate goal of this work is to fabricate a V-groove GaAs cell with improved absorptivity, high short-circuit current, and tolerance to particle radiation.
Leon, R. P.↗
Carbon Nanotube Tower-Based Supercapacitor
A supercapacitor system, including (i) first and second, spaced apart planar collectors, (ii) first and second arrays of multi-wall carbon nanotube (MWCNT) towers or single wall carbon nanotube (SWCNT) towers, serving as electrodes, that extend between the first and second collectors where the nanotube towers are grown directly on the collector surfaces without deposition of a catalyst and without deposition of a binder material on the collector surfaces, and (iii) a porous separator module having a transverse area that is substantially the same as the transverse area of at least one electrode, where (iv) at least one nanotube tower is functionalized to permit or encourage the tower to behave as a hydrophilic structure, with increased surface wettability.
Meyyappan, Meyya↗
Experimental Studies of Spray Deposition on a Flat Surface in a Vacuum Environment
Cooling of spacecraft components in the space environment is an on-going research effort. The electronics used in modern spacecraft are always changing and the heat flux is increasing. New, one-of-a-kind missions require new approaches to thermal control. In this research, under vacuum conditions, a pulsed water spray impinged on a small disc, while a high speed data acquisition system recorded the temperature histories of this copper disc. The water droplets froze quickly and accumulated on the disc as the spray continued. After the spray stopped, the frozen water that remained on the disc then sublimated into the vacuum environment and cooled the disc. This paper examines two important aspects of this process: 1) the difference in spray start up and shutdown in a vacuum environment versus in a standard atmospheric pressure environment, and 2) the water utilization efficiency in a vacuum environment due to the effects of drop trajectories and drop bouncing on the surface. Both phenomena play a role during spray cooling in a vacuum. This knowledge should help spacecraft designers plan for spray cooling as an option to cool spacecraft electronics, human metabolic generated heat, and heat from other sources.
Spray Cooling↗
Systems and Methods for Additive Manufacturing Processes that Strategically Buildup Objects
Systems and methods in accordance with embodiments of the invention implement additive manufacturing techniques that employ different sets of deposition characteristics and/or material formation characteristics during the additive manufacture of an object so as to strategically build up the object. In many embodiments, material used to build up an object is deposited at different deposition rates during the additive manufacture of the object, and the object is thereby strategically built up. In one embodiment, a method of additively manufacturing an object includes: depositing material onto a surface at a first deposition rate so as to define a first region of the object to be additively manufactured; and depositing material onto a surface at a second deposition rate so as to define a second region of the object to be additively manufactured; where the second deposition rate is different from the first deposition rate.
Hofmann, Douglas C.↗
Measuring coal deposits by radar
Front-surface, local-oscillator radar directly compares frequency of signals reflected from front and back surfaces of coal deposits. Thickness is measured directly as frequency difference. Transmitter is frequency modulated, so thickness is computed directly from frequency difference. Because front and back reflections are detected in combination rather than separately, masking of comparatively weak back signal is less problem. Also system is not sensitive to extraneous reflections from targets between transmitting antenna and coal surface.
Barr, T. A.↗