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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Origin of Ca-Al-rich inclusions. II - Sputtering and collisions in the three-ph8se interstellar medium

The theory put forward by Clayton (1977) for the formation of the Ca-Al-rich inclusions within C3 meteorites is extended to an evolutionary history in a three-phase interstellar medium. Widespread supersonic turbulence in the hot interstellar medium is maintained by supernova shock waves, giving rise to heavy sputtering of the refractory dust. Subsequent reaccumulation with varying dust/gas ratios or varying particle sizes produces isotopically fractionated Ca-Al-rich accumulates. It is thought that the Ca-Al-rich inclusions themselves are formed by the following sequence in the solar system: (1) cold accumulation of larger-than-average Ca-Al-rich particles containing supernova condensate cores into macroscopic (approximately 1 cm) Ca-Al-rich agglomerates, probably by sedimentation; and (2) fusion of the supernova condensates into macroscopic minerals by exothermic chemical reactions that begin when the accumulate has been warmed, thereby releasing energy from the unequilibrated forms accumulated from the interstellar medium.

Clayton, D. D.↗
NASA NTRS1984

The role of an intracrustal asthenosphere on the behavior of major strike-slip faults

Strain accumulation measurements adjacent to the San Andreas fault have indicated that the strain accumulation zone extends only a few tens of kms away from the fault. While the restricted zone of cyclic accumulation and release of elastic energy adjacent to major strike-slip faults has been attributed to a viscoelastic asthenosphere's damping effect, the narrowness of the San Andreas zone implies a thickness of the lithosphere that, at 10-20 km, may not be consistent with the relatively low surface heat flow measurements obtained. It is presently proposed that an upper elastic plate extends to a depth of 15 km, and that beneath this upper elastic plate is a soft, intracrustal asthenosphere exhibiting a viscoelastic behavior. A second elastic layer lies under this, followed by the asthenosphere. It is shown that the damping due to the intracrustal asthenosphere can explain the observed narrow zone of cyclic strain accumulation and release.

Turcotte, D. L.↗
NASA NTRS1984

Grain abundance in the primordial atmosphere of the earth

For models of planetary accumulation in the presence of solar nebular gas, the initial surface temperature of the earth is controlled by the grain opacity of the atmosphere. The surface temperature in turn controls the quantity of neon dissolved and trapped within the interior of the earth. To compare accumulation theory with observation, calculations have been made of the grain opacity expected to be associated with accumulation in a gaseous nebula. There are two parameters that are in principle determined by the theory, but actually are at present uncertain: the mean eccentricity(e) of the planetesimal swarm, and the fraction (xi) of the accretional energy that is expended in the release of grains into the atmosphere by ablation of the incoming planetesimal. It is found that if e is low (0.001), rather low values of xi (0.00001) are required to match the observed neon data. In contrast higher values of xi (0.1) are required for the most probable case with e = 0.01. For the high-eccentricity case (e = 0.1), xi must be greater than 0.01. The results show that avoidance of excess trapped neon of solar composition places restrictive, but not necessarily impossible, conditions on the parameters of the accumulation theory.

Mizuno, H.↗
NASA NTRS1985

The Origin of Regional Dust Deposits on Mars

Recently, additional evidence was derived from the Viking Infrared Thermal Mapper observations that allows a more complete model for the formation of Low Thermal inertia-high Albedo regions to be proposed. The first observation is that dust appears to be currently accumulating in the low thermal inertia regions. Following each global dust storm a thin layer of dust is deposited globally, as evidenced by an increase in surface albedo seen from orbit and from the Viking Lander sites. During the period following the storm, the bright dust fallout is subsequently removed from low albedo regions, as indicated by the post-storm darkening of these surfaces and by an increase in the atmospheric dust content over dark regions relative to the bright, low thermal inertia regions. Thus, the fine dust storm material is removed from dark regions but not from the bright regions, resulting in a net accumulation within the bright, low thermal inertia regions. Once deposition has begun, the covering of exposed rocks and sand and the accumulation of fine material on the surface make removal of material increasingly difficult, thereby enhancing the likelihood that material will accumulate within the low thermal inertia regions.

Christensen, P. R.↗
NASA NTRS1985

Automatic oscillator frequency control system

A frequency control system makes an initial correction of the frequency of its own timing circuit after comparison against a frequency of known accuracy and then sequentially checks and corrects the frequencies of several voltage controlled local oscillator circuits. The timing circuit initiates the machine cycles of a central processing unit which applies a frequency index to an input register in a modulo-sum frequency divider stage and enables a multiplexer to clock an accumulator register in the divider stage with a cyclical signal derived from the oscillator circuit being checked. Upon expiration of the interval, the processing unit compares the remainder held as the contents of the accumulator against a stored zero error constant and applies an appropriate correction word to a correction stage to shift the frequency of the oscillator being checked. A signal from the accumulator register may be used to drive a phase plane ROM and, with periodic shifts in the applied frequency index, to provide frequency shift keying of the resultant output signal. Interposition of a phase adder between the accumulator register and phase plane ROM permits phase shift keying of the output signal by periodic variation in the value of a phase index applied to one input of the phase adder.

Smith, S. F.↗
NASA NTRS1986

Initialization of a mesoscale model with satellite derived temperature profiles

The abilities of rawinsonde data and Tiros-N satellite derived temperature profile data to depict mesoscale precipitation accumulation are evaluated. Four mesoscale simulations using combinations of temperature, low-level wind, and low-level wind initialization were performed with the limited area mesoscale prediction system (LAMPS) model. Comparisons of the simulations with operational LFM forecast accumulations reveal that the LAMPS model simulations provide a better depiction of the observed precipitation accumulation than the LFM forecasts, and the satellite temperature profiles produce better mesoscale precipitation accumulation forecasts than the rawinsonde temperature data.

Kalb, Michael W.↗
NASA NTRS1990

Seasonal variations in Be-7 activity in the sediments of Cape Lookout Bight, North Carolina

The short-term sediment-accumulation rates in the interior of the Cape Lookout Bight (North Caroline) were determined using data on Be-7 activity distribution in the surface of sediments of the bight. Lack of a significant bioturbation in this lagoon made it possible to interpret variations in depth-integrated activity profiles of Be-7 as short-term accumulation events. The accumulation rates calculated from Be-7 activity profiles indicate that the delivery of particulate matter to the sediments of Cape Lookout Bight is not constant throughout an annual cycle, with the highest monthly accumulation rates being associated with north/northeast storm activity. Inputs were found to be highest during the late winter/early spring season, when the storm frequency is greatest.

Canuel, E. A.↗
NASA NTRS1990

Digitized synchronous demodulator

A digitized synchronous demodulator is constructed entirely of digital components including timing logic, an accumulator, and means to digitally filter the digital output signal. Indirectly, it accepts, at its input, periodic analog signals which are converted to digital signals by traditional analog-to-digital conversion techniques. Broadly, the input digital signals are summed to one of two registers within an accumulator, based on the phase of the input signal and medicated by timing logic. At the end of a predetermined number of cycles of the inputted periodic signals, the contents of the register that accumulated samples from the negative half cycle is subtracted from the accumulated samples from the positive half cycle. The resulting difference is an accurate measurement of the narrow band amplitude of the periodic input signal during the measurement period. This measurement will not include error sources encountered in prior art synchronous demodulators using analog techniques such as offsets, charge injection errors, temperature drift, switching transients, settling time, analog to digital converter missing code, and linearity errors.

Woodhouse, Christopher E.↗
NASA NTRS1990

Analysis and interpretation of Wide Field Planetary Camera outgas data collected in the temperature range from -20 C to -100 C

The data from the Wide Field Planetary Camera (WFPC) are analyzed to determine the absolute source-emission parameters and contaminant reemission parameters of outgassing mass accumulation. The data correspond to the mass accumulated on a -100 C quartz crystal microbalance and then desorbed at -50 C as a function of time. The parameters investigated include contaminant mass, first-order rate constants, and characteristic energies. The data are modeled in terms of a minimum number of species characterized by source-rate and reemission-rate parameters. The modeling technique is found to produce adequate fits, and the contaminants that accumulate at -100 C and desorb at -50 C do not accumulate at -50 C. The data analysis is found to be an adequate technique for assessing outgassing parameters for the prediction of WFPC internal contamination.

Barengoltz, Jack B.↗
NASA NTRS1995

Optoelectronic Particle-Fallout Sensor

Portable optoelectronic system monitors fallout of small particles (dust and fibers) onto surface at given location during extended time. Data on accumulated fallout downloaded from system to computer for display and analysis. Typical display is plot of signal proportional to amount of accumulated fallout as function of time and read to determine when contamination occurs. In many cases, possible to establish correlations between accumulations of particles and activities in vicinity. Also capable of signaling alarm in event contamination by fallout exceeds specified level. System made very inexpensively and used to monitor accumulation of dust and fibers associated with motion of air in variety of environments. Phenomena monitored indirectly by use of system might include circulation of air in buildings, and human and animal activity. Also serves as auxiliary intrusion monitor (though probably not real-time alarm) in sealed room because motion of intruder inevitably stirs up some dust.

Ihlefeld, Curtis↗
NASA NTRS1996

Recent Advances in Composite Damage Mechanics

The state of the art and recent developments in the field of composite material damage mechanics are reviewed, with emphasis on damage accumulation. The kinetics of damage accumulation are considered with emphasis on the general accumulation of discrete local damage events such as single or multiple fiber fractures or microcrack formation. The issues addressed include: how to define strength in the presence of widely distributed damage, and how to combine mechanical representations in order to predict the damage tolerance and life of engineering components. It is shown that a damage mechanics approach can be related to the thermodynamics of the damage accumulation processes in composite laminates subjected to mechanical loading and environmental conditions over long periods of time.

Reifsnider, Ken↗
NASA NTRS1996

Electrostatic Charging of the Pathfinder Rover

The Mars Pathfinder mission will send a lander and a rover to the martian surface. Because of the extremely dry conditions on Mars, electrostatic charging of the rover is expected to occur as it moves about. Charge accumulation may result in high electrical potentials and discharge through the martian atmosphere. Such discharge could interfere with the operation of electrical elements on the rover. A strategy was sought to mitigate this charge accumulation as a precautionary measure. Ground tests were performed to demonstrate charging in laboratory conditions simulating the surface conditions expected at Mars. Tests showed that a rover wheel, driven at typical rover speeds, will accumulate electrical charge and develop significant electrical potentials (average observed, 110 volts). Measurements were made of wheel electrical potential, and wheel capacitance. From these quantities, the amount of absolute charge was estimated. An engineering solution was developed and recommended to mitigate charge accumulation. That solution has been implemented on the actual rover.

Siebert, Mark W.↗
NASA NTRS1999

Standard Reference Rainfall Products Used in the TRMM Ground Efforts

The Primary goal of the Tropical Rainfall Measuring Mission (TRMM) Ground Validation (GV) effort is to provide basic validation of satellite-derived precipitation measurements over monthly climatologies. To this end, the Joint Center for Earth Systems Technology (JCET) at the University of Maryland, Baltimore County produces monthly rainfall accumulation reference products for each of the four primary TRMM GV sites. These products, standard methodology for deriving monthly, gauge-adjusted rainfall products, are utilized for each primary site. The monthly rainfall GV reference products are developed in discrete, modular steps with distinct intermediate products. These developmental steps, which will be fully discussed, include: (1) extracting radar data over locations of rain gauges, (2) merging rain gauge and radar data in time and space with user-defined options, (3) quality control of radar and gauge merged data by tracking accumulations from each instrument, and (4) deriving Z_R relationship from quality-controlled merged data over monthly time scales. A summary of all gauge statistics and GV rainfall reference products available for TRMM science users will be presented. Basic reference product results and trends involving monthly accumulation, Z-R relationship, and gauge statistics for primary GV site will be discussed. Finally, the sample impact on monthly rainfall reference products, through varying the time interval between intermediate rainfall accumulations, will be analyzed and presented.

Marks, David A.↗
NASA NTRS1987

The locations and amounts of endogenous ions and elements in the cap and elongating zone of horizontally oriented roots of Zea mays L.: an electron-probe EDS study

We used quantitative electron-probe energy-dispersive x-ray microanalysis to localize endogenous Na, Cl, K, P, S, Mg and Ca in cryofixed and freeze-dried cryosections of the cap (i.e. the putative site of graviperception) and elongating zone (i.e. site of gravicurvature) of horizontally oriented roots of Zea mays. Ca, Na, Cl, K and Mg accumulate along the lower side of caps of horizontally oriented roots. The most dramatic asymmetries of these ions occur in the apoplast, especially the mucilage. We could not detect any significant differences in the concentrations of these ions in the central cytoplasm of columella cells along the upper and lower sides of caps of horizontally-oriented roots. However, the increased amounts of Na, Cl, K and Mg in the longitudinal walls of columella cells along the lower side of the cap suggest that these ions may move down through the columella tissue of horizontally-oriented roots. Ca also accumulates (largely in the mucilage) along the lower side of the elongating zone of horizontally-oriented roots, while Na, P, Cl and K tend to accumulate along the upper side of the elongating zone. Of these ions, only K increases in concentration in the cytoplasm and longitudinal walls of cortical cells in the upper vs lower sides of the elongating zone. These results indicate that (1) gravity-induced asymmetries of ions differ significantly in the cap and elongating zone of graviresponding roots, (2) Ca accumulates along the lower side of the cap and elongating zone of graviresponding roots, (3) increased growth of the upper side of the elongating zone of horizontally-oriented roots correlates positively with increased amounts of K in the cytoplasm and longitudinal walls of cortical cells, and (4) the apoplast (especially the mucilage) may be an important component of the pathway via which ions move in graviresponding rots of Zea mays. These results are discussed relative to mechanisms for graviperception and gravicurvature of roots.

NASA Program Space Biology↗
NASA NTRS1989

Effects of root-zone acidity on utilization of nitrate and ammonium in tobacco plants

Tobacco (Nicotiana tabacum L., cv. 'Coker 319') plants were grown for 28 days in flowing nutrient culture containing either 1.0 mM NO3- or 1.0 mM NH4+ as the nitrogen source in a complete nutrient solution. Acidities of the solutions were controlled at pH 6.0 or 4.0 for each nitrogen source. Plants were sampled at intervals of 6 to 8 days for determination of dry matter and nitrogen accumulation. Specific rates of NO3- or NH4+ uptake (rate of uptake per unit root mass) were calculated from these data. Net photosynthetic rates per unit leaf area were measured on attached leaves by infrared gas analysis. When NO3- [correction of NO-] was the sole nitrogen source, root growth and nitrogen uptake rate were unaffected by pH of the solution, and photosynthetic activity of leaves and accumulation of dry matter and nitrogen in the whole plant were similar. When NH4+ was the nitrogen source, photosynthetic rate of leaves and accumulation of dry matter and nitrogen in the whole plant were not statistically different from NO3(-) -fed plants when acidity of the solution was controlled at pH 6.0. When acidity for NH4(+) -fed plants was increased to pH 4.0, however, specific rate of NH4+ uptake decreased by about 50% within the first 6 days of treatment. The effect of acidity on root function was associated with a decreased rate of accumulation of nitrogen in shoots that was accompanied by a rapid cessation of leaf development between days 6 and 13. The decline in leaf growth rate of NH4(+) -fed plants at pH 4.0 was followed by reductions in photosynthetic rate per unit leaf area. These responses of NH4(+) -fed plants to increased root-zone acidity are characteristic of the sequence of responses that occur during onset of nitrogen stress.

NASA Discipline Life Support Systems↗
NASA NTRS2005

Acclimation of Plant Populations to Shade: Photosynthesis, Respiration, and Carbon Use Efficiency

Cloudy days cause an abrupt reduction in daily photosynthetic photon flux (PPF), but we have a poor understanding of how plants acclimate to this change. We used a unique lo-chamber, steady-state, gas-exchange system to continuously measure daily photosynthesis and night respiration of populations of a starch accumulator [tomato (Lycopersicone scukntum Mill. cv. Micro-Tina)] and a sucrose accumulator [lettuce (Latuca sativa L ev. Grand Rapids)] over 42 days. AI1 measurements were done at elevated CO2, (1200micr-/mol) avoid any CO2 limitations and included both shoots and roots. We integrated photosynthesis and respiration measurements separately to determine daily net carbon gain and carbon use efficiency (CUE) as the ratio of daily net C gain to total day-time C fixed over the 42-day period. After 16 to 20 days of growth in constant PPF, plants in some chambers were subjected to an abrupt PPF reduction to simulate shade or a series of cloudy days. The immediate effect and the long term acclimation rate w'ere assessed from canopy quantum yield and carbon use efficiency. The effect of shade on carbon use efficiency and acclimation was much slower than predicted by widely used growth models. It took 12 days for tomato populations to recover their original CUE and lettuce CUE never completely acclimated. Tomatoes, the starch accumulator, acclimated to low light more rapidly than lettuce, the sucrose accumulator. Plant growth models should be modified to include the photosynthesis/respiration imbalance and resulting inefficiency of carbon gain associated with changing PIT conditions on cloudy days.

Frantz, Jonathan M.↗
NASA NTRS2007

The Cosmic Battery Revisited

We reinvestigate the generation and accumulation of magnetic flux in optically thin accretion flows around active gravitating objects. The source of the magnetic field is the azimuthal electric current associated with the Poynting-Robertson drag on the electrons of the accreting plasma. This current generates magnetic field loops which open up because of the differential rotation of the flow. We show through simple numerical simulations that what regulates the generation and accumulation of magnetic flux near the center is the value of the plasma conductivity. Although the conductivity is usually considered to be effectively infinite for the fully ionized plasmas expected near the inner edge of accretion disks, the turbulence of those plasmas may actually render them much less conducting due to the presence of anomalous resistivity. We have discovered that if the resistivity is sufficiently high throughout the turbulent disk while it is suppressed interior to its inner edge, an interesting steady-state process is established: accretion carries and accumulates magnetic flux of one polarity inside the inner edge of the disk, whereas magnetic diffusion releases magnetic flux of the opposite polarity to large distances. In this scenario, magnetic flux of one polarity grows and accumulates at a steady rate in the region inside the inner edge and up to the point of equipartition when it becomes dynamically important. We argue that this inward growth and outward expulsion of oppositely-directed magnetic fields that we propose may account for the approx. 30 min cyclic variability observed in the galactic microquasar GRS1915+105.

Contopoulos, Ioannis↗
NASA NTRS2009

Rotary drum separator system

A rotary phase separator system generally includes a step-shaped rotary drum separator (RDS) and a motor assembly. The aspect ratio of the stepped drum minimizes power for both the accumulating and pumping functions. The accumulator section of the RDS has a relatively small diameter to minimize power losses within an axial length to define significant volume for accumulation. The pumping section of the RDS has a larger diameter to increase pumping head but has a shorter axial length to minimize power losses. The motor assembly drives the RDS at a low speed for separating and accumulating and a higher speed for pumping.

Barone, Michael R.↗